1893.] NATURAL SCIENCES OF PHILADELPHIA. 239 



ures of Morse (I. c, V. minutd), of W. G. Binney, 9 in which, in har- 

 mony with the descriptions, the superior and cutting edges have 

 evidently been mistaken for each other. The jaw was somewhat 

 softened by strong caustic alkali, and the object drawn was evidently 

 extended by pressure. 



The radula, or lingual membrane, bears markedly different cen- 

 tral, lateral and marginal teeth. I found from 23-33 in a trans- 

 verse row, the former number in cyelophorella and perspectiva, the 

 latter in parvula. Morse counted 23 in minuta, W. G. Binney 21 in 

 pulchella. The difference may be partly explained by the rather 

 strong enlargement used by me, and partly by local variations. 

 The number of transverse rows varies from 63 in cyelophorella to 84 

 in exeentrica, and there is, as everywhere, some individual variation. 

 The size of the radula is not always in proportion to the shell. In 

 pulchella it is about 0*68 mm. long, and 0*24 wide ; in exeentrica 

 with the shell rather smaller, the dimensions were found 079 and 

 024 respectively. One transverse row measures O01-O011 in length, 

 while only O009 in perspectiva. 



The central tooth is small, its plate of attachment narrow, as long 

 as the row space, the posterior end somewhat wider in various 

 degrees. If not carefully examined, this may appear so in a higher 

 degree than it really is, since the plate is not exactly in the same 

 level. The side edges of the posterior end are curved up 

 and the angles are projecting like cusps. Plate VIII, fig. P, 

 shows a central tooth of V. parvula viewed in half profile with 

 these angles projecting almost beyond the level of the cusps. The 

 reflection at the front end is small, short, and bears 3 cusps, the 

 median about i-i as long as the plate. The side cusps are very 

 small, sometimes hardly perceptible. There are, as a rule, 3-4 per- 

 fect laterals, bicuspid, a larger mesodont and a small ectodont, the 

 former with a distinct free cutting point, the latter with just a trace 

 of it. The plate of attachment is almost as wide as long, and the 

 posterior part of the edge is curved up, as in the centrals, with the 

 angle projecting, also like a cusp. It doubtless acts as such, since 

 in the oldest teeth, where the cusps are nearly worn off, the same 

 is true of these posterior distal angles, including those of the central 

 tooth as represented in PL VIII, fig. G. On the fourth or fifth 

 tooth sometimes the remains of the two cusps are no longer coherent, 



y It is evidently the same cut, but in different position ; and it must be noted 

 that Morse, /. <r.,in all his figures, has the cutting edges above, while W. G. Bin- 

 ney in his Manual, has them directed downward. 



