92 MAZATLAN BIVALVES 



no fewer than eleven books without a synonym ! The yoiing 

 shell however has not been so well treated, being, according 

 to Jay and Eeeve, the C. latieostatum of Sotv. It certainly 

 suits exactly the description and measurements given m Proc. 

 Zool. Soc. 1833, p. 85. Mr. Cuming however states that C. 

 latieostatum is distinct and is the larger of the two ! The 

 young C. procerum moreover is not to be distingiushed trom 

 the figure of the young C. Panamense in Zrjol. Beech. Toy. 

 pi. 42, f. 7. which is described by Soto. Proc. Zool. Soc. 1833, 

 p. 85,'as only I'S in. long. The specimens in the Cumingian 

 Collection however are extremely large. The Mazatlan shells 

 are manifestlv of one species. It begins life nearly orbicular. 

 A young shell, b in. long, displays 7 close posterior ribs, 

 sharplv serrated at the margin, and with rows of tubercles on 

 their summits. The 10 ventral ribs are then subtriaugular, 

 rather sharp, minutely dotted at the top, and with the sides 

 and very narrow interstitial spaces finely decussated by con- 

 centric ridges which travel up and down over them. The 

 six anterior ribs are very much flattened, and faintly decus- 

 sated by the concentric lines.— GraduaUy both tubercles and 

 concentric ridges disappear, at an earher or later period ; the 

 ribs then become flattened, and at last on the anterior part 

 nearly pass away. The shell assumes a longer or broader 

 form,' with every gradation between. The number of ribs vanes 

 from 21—25, and does not depend on the shape. The colour 

 is whitish, variously spotted with reddish brown ; mside near 

 the posterior marffin, (which is very ringent,) of a rich brown- 

 ish purple. The ends of the ribs project beyond the margin of 

 the shell at the posterior ventral part, and beautifully mter- 

 lock. The side teeth are in a very slight curve from the car- 

 dinal. Epidermis thin, with very closely concentric ridges. 

 A broad specimen measures Zowfir. 2'5, lat.2"2, aZ^. 2'04. 

 The largest,, „ 3-07, „ 2-5, „_2-22. 



B:ah.—RcaS. Llejos, in coarse sand 4-6 fm. Cuming .—V&yi&, 

 D' Orhignt/.— Manama, rare, C. B. Adams.— S. W. Mexico, 

 pp, C — Mazatlan, Melchers. — Mazat\an: common; 

 L'pool Sf Havre Coll. 



Tablet 448 contains a minute imperfect valve.— 449. broad 

 variety, 5 pairs and a valve, young.— 450, do. 3 sp. adult.— 

 451, 4 sp. young, elongated form.— 452, 3 do. adult.— 453, a 

 curiously deformed valve. 



