252 PROCEEDINGS OF THE ACADEMY OP 



PECTINIBRANCHIATA. 

 Geomelania. Am. Journ. Couch., VII. 185, pi. xvii. fig. 7, 10. 

 Blaudiella reclusa, Guppy. Am. Journ. Conch., VII. ISo, pi. xvii. 

 fig. ~). 



Cyclotus stramineus, Rve. Am. Journ. Conch.,' I. 45, pi. v. fig. 1, 4. 

 T. Bland. Jaw and teeth. 



Megalomastoma cylindraceum, Chemn. Am. Journ. Conch., I. 45, 

 pi. V. ti-. 2. jaw. T. Bland. 



Megalomastoma Antillarum, Sowb. Same as last, fig. 3, teeth. T. 

 Bland. 



Megalomastoma bituberculatum, Sowb. Am. Journ. Conch., VI. 

 213, fig. 6. 

 Tulotomamagnifica, Conrad. Ann. Lye. K H. ofN. Y.,IX. 293, fig. 11. 



SCUTIBRANCHIATA. 

 Stoastoma pisum, Ad. Am. Journ. Conch., VII. 184. 



Helicina occulta, Say. Ann. Lye. N. H. of N. Y., IX. 287, fig. 8. 

 Am. Journ. Conch., VII. 29, pi. ii. fig. 6. 



Helicina orbiculata, Say. Am. Journ. Conch., VI. 214, pi. i.x. fig. 5, 



From the observations we have catalogued above, it appears that 

 the jaw cannot be depended upon as a generic character in the 

 genus Bulimus, as constituted in the second edition of Die Heliceen. 

 We have found it strongly ribbed, with ribs as described below in 

 Bulimulus, ribless, and ribless with a decided median projection 

 to its cutting edge. In Limicolaria the jaw is described with ribs, 

 we find it ribless in one species. In BuHviuhis, von Martens 

 describes the jaw as composite. We have shown it to be in one 

 single piece, though divided by delicate ribs into numerous plate- 

 like sections. The jaw is also very thin and transparent. This 

 form of jaw seems constant in Bidimulus. It is also found in 

 Cylindrella, 3Iacrocerainiis, Amphihulima^ Gaeoh's, and even in 

 Helix (H. turhiniformis). The tendency to an upper triangular 

 median plate is more or less seen in this form of jaw its greatest 

 development being in Cylindrella. 



In the genus Helix as constituted by von ]SIartcns, the jaw is 

 said to be ribbed, but we have found every variety of jaw except 

 that with an upper additional plate, and that with free imbricated 

 plates as in Orlkalicus. We believe, however, that the form of 

 jaw is constant in all the species of each section or subgenus of 



