60 



Polinices reclusianus, Strombus gracilior^ Cantharus pallidas, Nassarius 

 versicolor, Oliva incrassata, Olivella fletcherae, Hexaplex erythrostomus, 

 Mitra hindsii, Pleuroliria picta, Terebra specillata and Terebra variegata; 

 the lamellibranchs, Nuculana elenensis, Nuculana fastigata, Anadara 

 obesa, Chlamys circularis, Trachycardium panamense, Laevicardium elatum, 

 Laevicardium elenense, Megapitaria squalida, Chione mariae, Tellina tabo- 

 gensis, Macoma siliqua, Donax gracilis, Ensis californicus and Lyonsia 

 gouldii; the echinoids, Lovenia cordiformis and Moira clothe; and the 

 ophiuroid, Amphiodia occidentalis (Lyman). The family of mollusks with 

 the most number of individuals was certainly the Cardiidae, followed by 

 Veneridae and Turridae. Few polychaetes were noted and so far the only 

 ophiuroids and asteroids identified are: Amphiodia occidentalis and 

 Astropecton californicus. 



As mentioned previously, the 11 to 26 meter sand bottom assemblage 

 extends the length of the Gulf and probably to Ecuador, but the individual 

 species composition changes somewhat to the south. Some of the differences 

 between the north and south portions of this environment can certainly be 

 attributed to differing sampling devices. This is especially true with respect 

 to the decapod crustaceans, which were quite abundant in the northern re- 

 gion, collected mostly by dredge, and relatively uncommon in the southern 

 region collected by grab samplers. On the other hand, the most common 

 infaunal species were either of the same species or of the same genus in 

 both regions, illustrating the uniformity of the assemblage along the entire 

 coast. The contingency matrix did provide a basis for selecting stations 

 representative for the southern nearshore shelf by finding several groups 

 of closely associated species belonging to the stations shown on fig. 18. 

 Sampling devices used for those stations are on Table III. A list of the 

 living invertebrates from the 13 stations on fig. 18 is given in Table II, 

 which when compared with the list of species for the Tiburon region also 

 in Table II, gives an idea of both the similarity and uniqueness of the two 

 faunas. A number of typical mollusks from this environment (both north 

 and south) are illustrated on Plate IV, while others can be seen in Keen 

 (1958) or Olsson (1961). 



V. Intermediate shelf, 27 to 65 meters. 



The contingency matrix provided a very distinct set of stations, which 

 served as a basis for examination of the faunal associations in these depths. 

 Unfortunately, the northern portion of the intermediate shelf was sampled 

 primarily by shell dredges with a one meter opening (Table III), while 

 the southern part was sampled mostly by 12 and 3-meter wide otter trawls 



