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Among the mollusks taken during a ecological survey of Bahía de San Quintín, Baja California, noticed a single specimen of an unusual bivalve, the most closely related genus seems to be Orobitella, but so many points of difference was evident that the proposal for a new subgenus seems advisable.

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Parahemiurus noblei n. sp. (Trematoda: Hemiuridae) was described from of the stomach of the Pacific sardine Sardinops caerulea. Observations on living and mounted specimens of Tubulovesicula lindbergi (Trematoda: Hemiuridae) was discussed. A new locality and three new hosts for the latter species were recorded. The material for this study was obteined in November 1960 from fishes collected at Bahía de San Quintín, Baja California, México. A total of 83 fishes of sixteen different species were autopsied and their stomach checked for a digenetic trematodes. The worms were fixed with or without slight cover-glass pressure in warm Gilson´s fluid and stored in 70 per cent ethyl alcohol. All of the worms were prepared in the usual manner and were stained with Kornhauser´s Haematoxylin. Drawing were made with the aid of a camera Lucida and an upright microprojector; measurements were in millimeters.

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The present survey of Bahia de San Quintin in Baja California fulfills two primary purposes: a search for basic information on an unpolluted enclosure as near southern California as posible, and the initiation of comparative investigations. This report forms an introduction to a series of articles to be published on the geology, hidrography and benthic life of the bay, an includes those descriptive features not being treated elsewhere. For a bentic study a transect of samples was made across the northwestern marsh of the east arm starting on bare soil at the edge of the marsh next to a dirt road. Eighteen samples were taken 10 meters apart seaward of that point until the 19^th sample would have been underwater. This transect provides a record of the density of vegetation across the marsh. The samples were collected with a post hole digger having a capacity od 3080 cc, the sample forming a cylinder of 20 cm length and 14 cm diameter. The principal macroscopic invertebrate living in the marshes were the purple-striped reddish shore crab Hemigrapsus oregonensis, and the California horn- snail Cerithidea californica.

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Quantitative samples were taken using a Hayward bucket in 95 stations, in April 1960. Samples were washed through a screen with 32 openings to the inch (0.5 mm). The material retained on the screen was preserved in formaldehyde and sorted into groups. Later the polychaetes were separated. The faunal affinities of San Quintín bay were clearly related to southern California. All species but Scoloplos ohlini have been reported previously from southern California waters and 30 (60%) of these have been encontered previously in bays and harbors. One new specie Megalomma pigmentum, was found widely distributed in San Quintín. Present a list of 48 species known from Bahía San Quintín. Also discuss the relationship of polychaetes to sediments, the ocurrence of a species on a particular substrate type is given in percentage units. Six species of polychaetes constitute the dominant bay species on the basis of number of specimens.These are, in decreasing order of importance, Prionospio mamgreni, Exogone verugera, Cossura candida, Capitia ambiseta, Scoloplos acmeceps and Fabricia limnicola.

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Eight species from five families of polychaetes previously not reported for the area were found during three benthic samplings surveys in Bahía San Quintín in July and september 1981 and February 1982. The species include one orbiniid: Phylo felix, one paranoid: Aricidea suecica, three spionids: Prionospio heterobranchia sub. newportensis, Prionospio cirrifera and Pseudopolydora kempi, one megalonid. Megelona pitelkai and two capitellids: Notomastus (Clistomastus) tenuis and Mediostamus californiensis. For these species, their distribution is extended far southward to Bahía de San Quintín. A discussion about their biological meaning in the bay and some aspects of their biogeography is presented.

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Polychaete annelids collected in San Quintín Bay were analyzed. Thirty-nine stations were sampled with a geological type coree in December 1992, in depths of 2 to 6 m. A total off 677 polychaetes (17 families, 28 genera and 32 species) were recognized. Sixteen species and four gegera were recorded for the first time in the area. The best represented families were: Syllidae (124 species), Lumbrineridae (100), Flabelligeridae (75), Nereididae (74), Cossuridae (73), Spionidae (58), Capitellidae (49), Cirratulidae (44) and Maldanidae (29). The most abundant species were Scoletoma tetraura, Brada villosa, Cossura candida, Neanthes acuminata, Pionosyllis sp., Notostamus sp., Exogone lourei, Pronospio heterobranchia, Chaetozone sp. and Exogone dispar. The eastern arm of San Quintín Bay presented slightly higher values of species richness and polychaete abundances. Of the 28 families previously reported for this lagoon, 17 were found and the families Trichobanchidae and Apistobranchidae are added. To date, there are 81 polychaete species, belonging to 30 families, reported from San Quintín Bay.

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A 56 amphipoda species list, nine of them were not collected in grab samples. Discuss zoogeography of the species, and makes a comparison with Newport bay amphipods, and also compare San Quintín amphipod with the open sea. Shows a table with the habitat origins of the amphipods in Bahía San Quintín and a relationship of abundant amphipods to percent sand of substrate.

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The collections were obtained from grab samples and from formalin sea water washings of rocks and algae around the bay. A total of 87 lots of specimens resulted. There was a noticeable lack of parasitic Bopyridae, but the collections showed a reasonably diverified isopod fauna representing fifteen species from fifteen genera and eleven families. Over 26% of the species appeared to be new to science and four of these are described herein. Types were deposited in the U.S. National Museum.

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Samples were collected at 11 stations in July, September and December 1981, and February and May 1982. Thirty-nine species in 21 families of polychaetes were identified. The abundance increased in spring because of reproduction and recruitment. Five were the dominant species Exogone occidentalis, Pseudipolydora kempi, Scoloplos acmeceps, Prionospio heterobranchia and Neanthes arenaceodentata,The benthic community in Baía de San Quintín was found to be at or near equilibrium which may be the result of a relatively high resilience to disturbance. A qualitative assessment of the posible impact of domestic sewage on the infauna and an outline for the ecological mangement of the bay are presented.

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The marine littoral tubificid Tectidrilus diversus Erséus, 1982 is reported for the first time in México, in Bahía San Quintín, Baja California. The new record is a range extension of the species, which has been previously known on the Brittish Columbia, Washington and California coasts.

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De un total de 19 especies epifaunales recolectados en las praderas de Zostera marina frente al campo El Chute, en la Bahía de San Quintín B.C. los crustáceos anfípodos de la Familia Gammaridea fueron predominantes. Se analizaron muestras de Abril, Julio, Agosto, Septiembre, Noviembre y Diciembre de 1993. Se presenta una descripción taxonómica, claves utilizadas para su identificación, distribución, ecología además de figuras originales de cada especie. Se incluyen igualmente observaciones personales y otras ya publicadas por expertos en el tema con el fin de facilitar la identificación taxónomica.

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