CRETACEOUS FOSSILS. 91 



PERISSOLAX, Gabb. 



P. BREVIROSTRIS, 11. 8. 

 PI. 19, Pig. 43. 



Shell short, robust, thick ; spire of moderate height ; whorls 

 five, enveloped in such a manner that only the upper surface of 

 the preceding whorls is visible. Suture distinct, bordered below 

 by a carina, or sometimes a mere swelling of the upper edge of 

 the whorl. Apical angle variable, sometimes uniform from the 

 apex to the angle of the last whorl ; in other specimens it is irregu- 

 larly convex, from each whorl making the angle more acute. In 

 one specimen the first two whorls are very acute, and the rest 

 unusually obtuse. Surface biangular, sometimes with a smaller 

 ridge below ; marked on each angle by a row of large blunt tuber- 

 cles, usually placed opposite each other, and each series connected 

 by a low, rounded rib. These, as Well as the rest of the shell, 

 except the canal, are crossed by numerous variable revolving ribs, 

 which are largest in the deep excavation just below the lower 

 carination. Mouth simple, wide above, suddenly narrowed into 

 the long, slender canal in advance. Columella slightly incrusted 

 and faintly undulated in the middle. 



Figure, natural size* 



Localities : Tuscan Springs, Martinez, Pence's Ranch, &c. ; very characteristic 

 of Division A. 



The only marked variation in this species is in the somewhat irregular manner 

 in which the spire is enveloped hy each successive whorl. A slight difference 

 may be found in the presence or absence of the third (lowest) row of tubercles. 

 It is rare to find them entirely absent. 



I place this shell in the genus Perissolax, nobis, although the canal is unusually 

 short ; a character which approaches that group to the true Fusus, and of which 

 it may probably be considered only a subgenus. 



