176 BuivI^ETlN 31 176 



Gaines, Ga. ; Montgomery, I^a. (Jackson). 



Spisula decisa Conrad, PI. 54, Fig. i 



Madra decisa Con., Foss, Sh. Tert. Form., 1833, 42. 



M. decisa Con., Amer. Jour. Sci., vol. i, 1846, p. 216, pi. 2, fig. 3. 



Spisula decisa Dall, Trans. Wag., Ill, 1895, p. 896. 



Conrad' s best chai-acterization (Amer. Jour. Sci. ). — Triangular, ven- 

 tricose, uinbonial slope angular, slightly carinated, posterior slope depressed, 

 with a line somewhat bifid or double from beak to base, and short oblique 

 prominent lines on the upper portion of the valves ; cardinal fosset large 

 and profound, the anterior tooth adjoining it triangular, with a deep pit on 

 each of the three sides. Claiborne, Ala. 



This very rare species has not been found entire. I have only one 

 fragment, and the hinge of this is perfect enough to exhibit the fissure in 

 the hinge line under the apex, which characterizes the genus Scissodesina . 



We have little hesitation in referring the fragment we have 

 of a hinge line to this species though the umbonal slope can 

 scarcely be described as "carinated", nor do we quite under- 

 stand "the fissure in the hinge line". 



Type. — A mere fragment in the Phila. Acad. Conradian Col- 

 lection. 



Our specimen is likewise from the Claiborne sand and is now 

 at Cornell. 



Spisula decisa var. palmaris, n. var., PI. 54, Figs. 2-6 



With such fragmentary material at hand it is difficult to de- 

 cide whether the typical decisa from the Claiborne sand should be 

 classed as one and the same species with the St. Maurice material. 

 The Claiborne sand fragments indicate a very deep shell cavity, 

 and show a large, robust beak, very tightly incurving and some- 

 what twisted. The St. Maurice specimens show a more pointed 

 and erect beak with seemingly a slightly less capacious shell cav- 

 ity. We seriously doubt the propriety in uniting these differently 

 appearing forms without calling attention to certain well-marked 

 differences. 



Under var. palmaris, accordingly, we would place the inter- 

 nal casts and molds from the base of the Claiborne bluff, such as 



