GEOLOGY AND PALEONTOLOGY OF THE SCHOHARIE VALLEY 199 



Fig. 133 Pentagonia unisulcata 



[fig. 132], easily recognized b}^ its peculiar form; A try pa 

 reticularis [fig. 133], generally quite robust ; and P e n - 

 tamerella a rat a [fig. 100], a pentameroid shell with 

 strongly arching beak as in Gypidula, but with sinus in the 

 pedicle valve and cor- 

 responding fold in the 

 brachial valve, though 

 these are not always 

 pronounced. Strong 



bifurcating rounded 

 plications cover all ex- 

 cept the upper part of 

 the beak. Finally 

 among the more com- 

 mon species should 

 be named A m p h i - 

 genia elongata [fig. 134], which when full grown is a 

 large, terebratuloid shell not unlike Kensselaeria but proportion- 

 ally wider. The internal characters are pentameroid and the sur- 

 face is covered with fine 

 radiating striae. 



Among the gastropods 

 the following are com- 

 mon and characteristic : 

 Platyceras dumo- 

 sum [fig. 135], an 

 extremely spinose shell, 

 with the apex enrolled. 

 The form varies from sub- 

 cylindric in the adult to extremely ventrioose. Diaphoros- 

 toma lineatum [fig. 136], a close coiled, nonumbilicate, 

 low-spired shell, with uniformly enlarging suborbicular aperture, 

 and fine spiral striae cancellated by the lines of growth. 

 Euomphalns decewi [fig. 137] , a flat coiled shell with 

 the whorls enrolled in nearly the same plane and barely touch- 

 ing, and with a strong carina on the upper part of the last whorl, 



Fig. 133 A t r y p a reticularis 



