376 Certain Shells in the British Museum. 



hinder slope reddish brown, separated by a distinct line. Umbones 

 brownish. 

 Var. ? ovate, trigonal. The anterior lateral tooth rather larger and 

 thicker. 



Inhabits . 



* Shell trigonal. Hinder Slope flattened. 



3. Mulinia lateralis; Mactra lateralis Say. (Fide Spec. Say.) 

 Inhabits North America. 

 i^Tto 4. Muliwa donaciformis n. s. Shell trigonal, ventricose, white; eovered 

 with a thin periostraca. Hinder slope flattened, keeled on the edge. 

 Inhabits South Sea. — Capt. Beechey's Expedition. 

 5. Mulinia edulis ; Mactra edulis King, in Zool. Journ., v. 335. Shell 

 (? young) ovate, thin, white, smooth j covered with a thin olive or reddish 

 periostraca, forming two raised edges on the hinder slope. Hinder slope 

 white. Lateral teeth short, triangular. 

 Inhabits Port Famine. — Capt. King. 



\. ** Hinder Slojye simple. 



&P 6. Midinia Byronensisn.s.f.5. Shell ovate, slightly triangular, white, rather 

 solid. Lateral teeth thick, rounded. Young lateral teeth thinner. 

 Inhabits South America. — Capt. Lord Byron. 

 7. Mulinia exdlbida. Shell ovate-oblong, white, rather thick. Umbones 

 subanterior. The lateral teeth short, thick. Anterior one subtubercular. 

 Inhabits South America. — Capt. P. P. King. 



VI. Gna'thodon Gray, Rang, Sow. Ra'ngia Desmoulins. 



Shell ovate, trigonal, solid, white; covered with a brown cartilaginous 

 periostraca. Margin acute, simple. Umbones often eroded. Hinge teeth 

 two in each valve ; the front of the left 

 valve larger, bifid ; the hinder of left, and 

 those of right, valve, equal, small, simple. 

 Hinder lateral teeth very long, compressed, 

 transversely grooved; the front one 

 shorter, rugulose; dilated, and subtrigonal 

 above. Siphonal inflection short, half- 

 ovate. Cartilage internal. Ligament in- 

 ternal in the upper edge of the very deep 

 cartilage pit, which is often open at the 

 top by the abrasion of the apex. Animal, 

 siphons short, separate. Mantle's lobes united in front. It resembles 

 Cyrena Cor. in the form of the anterior lateral teeth, and agrees with 

 Mulinia in having an internal ligament. 



1. Gndthodon cunedta Gray {fig. 34.) Sow. Gen. ; Rangia cyrenoides Des- 

 moulins Act. Lin. Soc. Bord., iv. 58. ; Clathrodon cuneata Conrad in 

 Silliman's Journal, from my MSS. 



The city of Mobile, in North America, Mr. Conrad informs us, is built 

 on vast beds of this shell, and it exists on all of the alluvial coast of the 

 Gulf of Mexico, between Pensacola and Franklin, in Louisiana. Desmou- 

 lins says his specimen was brought from Lake Vonchartraen, in East 

 Florida, near New Orleans, which is, probably, saltish water. I described 

 my specimen from two single valves, picked from a ballast heap in Canada, 

 to which it was, probably, brought from the Gulf. The description was 

 sent to America many years ago, but it was not published, because the 

 American conchologists considered it as a Cyrena! and call it Cyrena 

 truncdta of Lamarck ! in their cabinets. 



