28 AMERICAN JOURNAL 



ON THE LINGUAL DENTITION OF CLAUSILIA TRIDENS, 



CHEMNITZ. 



BY THOMAS BLAND AND W. U. BINNEY. 



Clausilia tridens, Chemn., occurs in Puerto Rico only, and no 

 other species of the genus has been found in the West Indies. 

 The jaw and lingual membrane here described were received from 

 Mr. Robert Swift. 



Jaw slightly arcuate, low, long, of almost equal height through- 

 out ; ends slightly attenuated, bluntly truncated ; anterior sur- 

 face without ribs; cutting edge with a blunt median projection. 

 Figure 4 is drawn from a photograph taken by our friend Mr. 

 Sam. Powel. It will be seen that the cutting edge is developed 

 beyond the well marked median beak. This extension is thinner 

 than the rest of the jaw, and can, we believe, scarcely be normal. 

 Should it prove to be constant in the species, the concave mar- 

 gin can hardly be said to have a median projection, but still the 

 well marked beak upon the inner line will show the species to 

 be related, by the characters of its jaw, to the subfamily Pu- 

 pinre. (See Land and Fresh Water Shells of N. A., Part I, 

 p. 223). 



Lingual membrane short and broad, composed of numerous 

 rows of about 30 — 1 — 30 teeth each. Centrals long, narrow, 

 incurved at sides, concave and either excavated or thinned at 

 base, rounded at top, and with a recurved, small, blunt apex. 

 Laterals shorter and broader than the centrals, their base cut 

 away for two-thirds their length nearest the centrals, their sides 

 parallel, curving outwards from the centrals, the top rounded or 

 indented ; apex recurved, produced into a stout tri-lobed or bi- 

 lobed denticle, the central or larger lobe bearing a stout, pro- 

 longed, conical point. At about the twelfth lateral the teeth 

 commence to change gradually into the marginals, the extreme 

 form of which are subquadrate, wider than high, broadly 

 recurved into an oblique, irregularly denticulated apex ; the mar- 

 ginals decrease rapidly in size as they pass outward towards the 



