26 ACM^A. 



A. FAScicuLARis Menke. PI. 6, figs. 50, 51, 52, 53. 



Shell rather thin, depressed, oval ; surface closely radiately stri- 

 ated, the strife low, often obsolete but indicated by light dark lines. 

 " The prevailing tints are a reddish-brown outside, more or less 

 mottled or striped with white ; inside a prevailing white, more or less 

 penciled or fretted with brown, and a border, sometimes white with a 

 tessellated penciling of brown ; sometimes a delicate fawn shading 

 into a pinkish or slightly greenish tinge, with or without penciling. 

 The body mark is of a dark lustrous brown, or very light with a 

 greenish tinge, or nearly absent. It is large for the size of the shell, 

 more or less removed from the margin. In shape, A. fascicularis is 

 much longer, and generally smaller than discors. The standard 

 color of J., mesoleuca is green, of A. fascicidaris red. In A. meso- 

 leuca the markings are laid on with stripes and patches, in A. fascic- 

 ularis with very fine penciling. In the latter the outline of the 

 body mark is much more regularly gathered up into points with 

 concave margins between, the points often making regular lines radi- 

 ating from the center. The surface of A. mesoleuca is covered with 

 granulose ribs with soft interstices and a very thin smooth epidermis ; 

 that of A. fascicidaris is very much more finely marked, showing under 

 the glass, smooth ribs with the interstices extremely finely cancel- 

 lated Avith very close, slightly rugose concentric strife, covered with 

 an extremely thin, rather velvety epidermis. The surface of A. fascic- 

 ularis is much more generally abraded ; and as the young shells were 

 not uncommon in the Spondylus and Chama washings, while not one 

 was found of A. viesoleuca, it is presumed that their station is different. 

 The apex is sometimes brown, sometimes white ; and in the smallest 

 specimen, "035 by "025, shows no trace of being spirally recurved. 

 The young shells are known by their finely cancellated texture and 

 delicately reddish penciling ; and generally, by a white spot pro- 

 ceeding from the apex posteriorly bounded by red lines. In all 

 stages it is thin, and very glossy within." ( Cpr.) 



Length 27, breadth 21, alt. 6 mill. 



Mazatlan, and Gulf of California generally. 



A. fascicidaris Mke. Zeitschr. f. Mai. 1851, p. 38. — Cpr. Mazat. 

 Cat., p. 255. — Dall, Amer. Journ. Conch, vi, p. 253, t. 14, f. 11 

 (dentition). — A. mutabilis Mke, in part, 1. c, p. 37. — Patella opea 

 RvE., Conch. Icon., f 79, teste Cpr. 



A beautifully penciled species, allied to S. mesoleuca. The 

 synonymous P. opea of Reeve as represented on pi. 6, figs. 52, 53. 



