TRANSACTIONS OF WAGNER 

 1462 



TERTIARY FAUNA OF FLORIDA 



a single raised radial keel which in profile appears like a spur or small, blade- 

 like prominence. These characters are so obvious as to afford excellent data 

 for grouping the various species in accordance with their genetic relations. 

 It should not be forgotten that the Abbe Dupuy in 1843 suggested a classifica- 

 tion of the Sph&ria on a similar basis, which was met with undeserved scorn 

 by Bourguignat, whose less scientific arrangement for the time prevailed. 



The shell of Corneocyclas has the anterior end longer than the posterior, is 

 concentrically feebly sculptured; there 'are no crenulations of the inner mar- 

 gins, and while the lunule and escutcheon are sometimes clearly defined by a 

 delicate line they are hardly visible except under strong magnification and are 

 lost by the slightest wear. The ligament, as in Sphcerium, is inset, and in most 

 cases only the narrowest chink, if any, exists above it between the edges of the 

 valves. In a few species, notably C. virginica Gmelin, a portion of the ligament 

 is external, but in most of them it may be fairly called internal. This is 

 another larval character, the protoligament being situated between the valves ; 

 whence, in most pelecypods, it migrates upward; while in those forms in 

 which it is called internal it has redescended, and not merely kept its original 

 emplacement. But in the Sphariida it is probable that it has never emerged 

 from between the valves to a greater extent than we find it at present. 



The hinge of Corneocyclas consists of paired laterals, anterior and posterior, 

 in the right valve, and single ones in the left valve; these in the larger and 

 more solid species often show a faint striation or granulation, but in the ma- 

 jority are smooth. The cardinals in the best developed forms have become 

 independent of each other and of their lateral laminae, and comprise two teeth 

 in each valve, of which the posterior left and anterior right cardinals are slender 

 and entire, the two others thick, subtriangular, and bifid. But in the great 

 majority of the group, in which development has been arrested at an earlier 

 stage of the hinge, the two right cardinals remain connected and are usually 

 treated as a single sinuous or angular tooth, while the larger cardinal of the 

 left valve remains of a hook-shape with more or less of its posterior limb 

 attached, so that one cardinal appears below the other to some extent, instead 

 of behind the other. In one small group of species traces of the connection 

 between the original anterior lateral laminae and the anterior cardinals still 

 persist, as in C. pusilla Gmelin. In many cases the compound right cardinal 

 becomes comma-shaped, with its thick posterior end bifid or clavate. 



The foot is elongate and subconic, byssiferous in young stages ; the mantle 

 edges free except for the anal siphon, and there is no sinuation of the pallial 

 line. All the species are viviparous. 



