1849.] SHARPE ON THE GENUS NERIN^A. 113 



are wide, increasing regularly. Suture in the middle of a rounded 

 ridge, which is broader than the conca^dty of the whorl. Columella 

 hollow, the umhilicus occupying about one-fourth of the diameter of 

 the shell. Mouth suhrhomboidal, with the outer lip indented. One 

 fold in the interior, on the top of the whorl, curving outwards. 



Sutural angle 85°. Basal angle 100°. Greatest diameter seen 

 1| inch. 



Found in limestone near the base of the subcretaceous series at 

 Alenquer. 



Readily known by the regular annulations of the exterior, and by 

 the single fold at the top of the nearly square interior of the whorls, 

 in which it resembles N. depressa, N. pi/ramidalis, and N. suhpyra- 

 midalis. 



Plate XIII. fig. 1 a. Exterior. 



Fig. 1 b. Section. 



Nerin^a turbinata, n. s. 



Shell conical, with a large umbilicus. Spire increasing regularly 

 with an angle of about 35° ; whorls about ten, concave in the middle 

 and crossed by slightly oblique irregular lines of growth. Suture in 

 the middle of a projecting ridge which is irregularly crenulated by the 

 lines of growth. Mouth suhrhomboidal, with a callosity inside the 

 outer lip and a fold on the inner lip. Columella hollow, the umbili- 

 cus occupying one-third of the diameter of the shell. Two folds in 

 the interior ; one on the middle of the outer lip, the other a little 

 below it on the columella. In the lower whorls the folds are nearly 

 equal, and a section of the space left is a rude representation of an 

 hour-glass ; in the upper whorls the outer fold becomes much larger 

 than its fellow. 



Sutural angle about 90°. Basal angle about 95°. Total length 

 If inch. Diameter f of an inch. 



Found in limestone near the base of the subcretaceous series three 

 miles south-west of Alenquer, and between Torres Vedras and Sobral. 



In external form and markings this shell so exactly resembles 

 Trochus Astierianus of D'Orbigny, Terr. Cret. pi, 176. f. 16, 17, that 

 they might easily be confounded ; but the latter species is figured 

 without an umbilicus, and is described as not umbilicated (p. 182). 



Our species is allied to N. Renauxiana, D'Orb., by its hollow colu- 

 mella, and it resembles the young state of that species in its spiral 

 angle ; but it has a fold less on the columella. About twenty speci- 

 mens have been seen, all so nearly of the same size that they may be 

 presumed to be full-grown shells. 



Plate XII. fig. 2 a. Exterior. 



Fig. 2 b. Section of the interior of another specimen. 



Subgenus 4. Ptygmatis. 

 Nerin^a Eschwegii, n. s. 



Shell turreted, cylindrical, smooth. Whorls numerous, nearly 

 equal, convex, equal in height to half the diameter of the shell. 

 Sutare running in a marked depression. Columella solid, small. 



