412 NEW GENUS AND SOME NEW SPECIES 



which are minutely waved ; these lines are continued over the 

 umbonial slope. The irroratus is covered over the whole 

 disk with dark green spotted lines, running in a sweep from 

 the beak to the margin and lying close to each other. 



The following species have broad interrupted rays, which 

 in some instances make rows of square spots : viz. planulatus, 

 scalenius, verrucosus (when young), and patidus. 



The donaciformis and zig-zag have diverging rays formed 

 more or less distinctly by zig-zag lines. The cylindricus, 

 metanever, and triangularis are singularly and most beauti- 

 fully marked with dark green spots in the form of an arrow 

 head, the point directed to the margin. The first and last 

 possess the most; in the others it can only be distinguished 

 in very fine or young specimens. The marks sometimes ex- 

 ist in a confluent state, and rays are consequently produced. 

 They are most prevalent in the cylindricus, and vary from 

 the length of a quarter of an inch to a mere point ; in the tri- 

 angularis they are more generally confluent. Some speci- 

 mens of cylindricus are so much charged with these arrow- 

 headed marks as almost to obliterate the yellow ground of 

 the epidermis, and cause the valves to appear at first sight of 

 an uniform dark green. 



The remainder of the American species described are with- 

 out epidermal markings, and I shall divide them, as it is ex- 

 tremely difficult to designate their shades, into blackish, 

 brownish, and yellowish. The ater, tuberadatus, circulus, 

 and gibbosus* are blackish. The circulus is peculiar in hav- 

 ing the posterior slope yellowish. The parvus, torsus, plica- 

 tus, mytiloides, sesopus, subtentus, verrucosus, ellipsis, rubi- 

 ginosus, are brownish. Some of these, however, vary much. 

 The torsus is found sometimes yellowish, and when young 

 almost black; the posterior slope is, however, universally 

 yellowish. Large and old specimens of the plicatus are 

 quite black; the young are light brown. In the mytiloides 



f The young gibbosus is sometimes very obscurely raved. 



