52 MAZATLAN BIVALVES 
Brazils, Rio de Janeiro, Patagonia; “Baie Blanche, Voy. 
no. 130,” D’ Orbigny.—Mazatlan ; one specimen tas sent, 
quite fresh, papered up along with the Semeles; L’pool Col. 
Tablet 213 contains the specimen. 
80. Macrra (Muuinia) aneunata, Gray, ms. 
Rve. Conch. Icon. pl. ix. sp. 34. 
This species is known at once from the young of M. exoleta 
by its stout, subtrigonal growth, the shortness of the anterior 
portion and the rather distant umbos. The epidermis is extreme- 
ly thin, gradually passing off towards the anterior portion, as in 
M. exoleta; but differs in being loose, lying in irregular concen- 
tric folds, fringed at the posterior angle. The hinge teeth are 
large and prominent; lateral ones very finely shagreened. 
The muscular impressions are singularly close to the margin 
of the shell; pallial sinus small, oval. ? Can this be the M. 
donaciformis of C. B. Ad. (Pan. Shells p. 293,) as the true 
M. donaciformis is given by Ave. as from N. Zealand.* This 
shell seems also to have relations with M. goniata, Gray, ms. 
(Proc. Zool. Soc. 1854, p. 70,) and with M. carinulata, Desh. 
(Proc. Zool. Soc. 1854, p. 67: Rve. Conch. Icon. pl. 10, sp. 38), 
both from the gulf of California. Long. 2°25. lat. 3°05, alt.1°78. 
Hah.—Gulf of California, Reeve.—S. W. Mexico, P. P. C— 
Mazatlan ; a very few specimens were found with M. exoleta: 
T’pool Col. 
Tablet 214 contains two specimens; one young with the 
epidermis perfect ; the other adult. 
Genus GNATHODON, Gray. 
Gnathodon, Gray, Am. Journ. of Science ? 1830.—Rangia, 
Desmoul. Ac. Soc. Lin. de Bord. 1831.—Clathrodon, Conv. 
Sillim. Amer. Journ. 1833. — 
81. GnatHopon (Rangia) TrRIgona, Petit. 
G. t. solidd, subtrigonali, alba, epidermide flavescente, pos- 
terius rugosa, indutd ; plus minusve’ inequilaterali, parte pos- 
teriori angulo ab umbonibus decurrente indistincte separata ; 
umbonibus subcentralibus, distantibus, non spiraliter recurvis ; 
* Reeve however, under M. carinulata, sp. 38, speaks of M. donaciformis as 
from the Gulf of California. ? Is it authenticated from both localities. 
