178 PALEONTOLOGY OF NEW-YORK. 



Fig. 5 a. Front view of a nearly perfect specimen, showing the form of the aperture, b. Back view. 



Fig. 5 c. Front view of a specimen with the last volution broken off behind the aperture, giving it a 

 different form. 



Fig. 5 d. View of an imperfect specimen, showing the direction of the striae. 



Fig. 5 e. An enlarged view of the same. 



Fig. 5 f. A smooth cast from crystalhne limestone, scarcely preserving the upper carination in an 

 obscure angle. These specimens are of the ordinary size of the shell in most localities. 



Fig. 5 g. View of a large imperfect specimen, still preserving the strice upon the surface. 



This specimen preserves the same form and proportions as the others figured ; but al- 

 though retaining the shell, it does not present the double mesial band, a single obtuse carina 

 being all that is visible. The sharp lines on either side have doubtless been obliterated with- 

 out removing the vertical striae. 



Fig. 5 A. A portion of the same enlarged. 



Position and locality. This species occurs more frequently in the lower shaly portions of 

 the Trenton limestone at Mitldleville. It is found occasionally in the higher crystalline 

 part of the same rock at that place. The cast fig. 5 _/ is from the higher part of the same 

 rock at Turin in Lewis county. The larger specimen 5 g is from the compact lower part 

 of the rock at Watertown. (State Collection.) 



230. 7. MURCHISONIA TRICARINATA (w. 5j5.). 



Pl. XXXVIII. Figs. 6 a, b, c. 



Subfusiform ; spire elongated, acute ; volutions five or more, gradually expanding below, 

 tricarinate, the central carina more prominent than the other two ; aperture suboval, 

 acutely extended below ; surface marked by sharp prominent striae, which are distinctly 

 undulated in passing over the central carina ; umbilicus none. 



This species somewhat resembles the last, but the spire is more extended and gradually 

 enlarging below ; the central carina is not margined by two smaller ones, and both the 

 carintE and striaj are stronger and more distinctly elevated above the surface. The form of 

 the aperture, so far as can be seen, is more distinctly oval, and not so straight upon the 

 pillar lip. The shejl is somewhat distorted by pressure, and therefore cannot be perfectly 

 represented. 



Fig. 6 a. View of the back of the shell. 



Fig. G b. Front view, showing the aperture, which is imperfect on the outer side. 



Fig. 6 c. This fragment belongs apparently to the same species, but the striae are much better preserved, 

 and the carinte sharply projecting. The striae between the suture and upper carina are 

 directly vertical ; between the first and second carinas they bend backwards, making an 

 acute retral angle on the mesial carina, below which they again turn forwards, and, in 

 passing the lower angle, bend backwards. These characters are clearly distinct from cither 

 of the other species described ia this place. 



Position and locality. This species occurs at Mineral Point ( Wisconsin) , associated with 

 Pleurotomaria vmbiiicnta and several other Trenton limestone fossils. 



(Cabinet of Mr. Conrad.) 



