176 PALjBONTOLOOr OF NKW-YOKK. 



226. 14. PLEUROTOMARIA INDENTA ( n. sp.) . 

 IV XXXVIII. Fig. a o. 

 Plevrotomaria. Emmokb, Geol. Report, 1842, pag. 396, fig. 5. 



Obliquely depressed conical ; spire short, acute ; volutions about three, rapidly enlarging 

 towards the aperture ; the last one, composing the greater part of the shell, is ventricose, 

 biangulated above and rounded below ; angles subnodulose, with indentations between 

 the two and below the lower one ; aperture rounded or transversely broad oval ; surface 

 marked by fine striae. 



This species usually occurs in the form of casts of the interior, scarcely preserving any 

 remains of the surface markings. It is readily distinguished by its small acute spire above 

 the last volution, which is distinctly nodulose on the two angles. In this character, it difTers 

 from any other in the Trenton limestone. 



Position and locality. This species is known only in the black limestone at Watertown, 

 being the lower portion of the rock at this place. (State Collection.) 



227. 15. PLEUROTOMARIA AMBIGUA («.«;».). 



Pl. XXXVUI. Figs. 3 a, b. 



Depressed conical, width about equal the height ; spire short, obtuse ; volutions few 

 (three or four), rapidly increasing towards the aperture, subangular, ventricose; the last 

 volution distinctly bicarinate on the outer edge, upper ones with a single carination near 

 the lower side ; suture canaliculated ; aperture subquadrate, with the angles rounded above 

 and expanding below ; umbilicus small , scarcely distinct. 



This species resembles in many respects the Pleurotomaria umbilicata, but differs in some 

 important particulars. The spire is higher, each volution being less compressed vertically ; 

 the space between the two marginal angles of the volution is less, and these angles less 

 prominent. The umbilicus is scarcely distinct, and the aperture is less extended transversely, 

 and angulated below, approaching in this respect to Muhchisonia. 



I have but a single specimen sufficiently perfect to figure, and this one is somewhat 

 distorted from pressure, and the aperture imperfect. 



Fig. 3 a. View of the back of the spire. 



Fig. 3 b. Front of the same, showing the apertura 



Position and locality. In the higher shaly limestone at Adams, Jefferson county, asso- 

 ciated with the preceding species. (.state Collection.) 



