I. i; PA 1)1 DJE. 



STROBILEPIS, n. a. (J. M. C). 

 Strobilepis spinigera, n. sp. 



PLATE XXXVI, PIGS. 20-22. 



\ SPECIMEN from the soft shales of the Hamilton group, in a fair state of 

 preservation, presents features whose homologies are not at present well 

 understood and do not permit a satisfactory interpretation of their taxonomic 

 relations. The specimen itself is here described as it appears, and this descrip- 

 tion must serve temporarily as the diagnosis of the species: 



The capituujm consists of a conical terminal plate 5 mm in height, having a 

 nearly circular base, 10 mm. in diameter, against which lie the final plates of 

 three vertical ranges, one at either side and one in the middle of the speci- 

 men. Of these three ranges, the plates composing those at the sides are of 

 about the same size, while those on the central range are much smaller. 

 All these plates have, however, about the same general trihedral form, but 

 differ somewhat in details. 



The first plate in the left vertical range is abruptly truncated on its anterior 

 margin, from apex to base; from the apex backward sharply angulated and 

 sub-carinate near the apex, becoming broader as it approaches the margin. 

 This plate is quite unsymmetrical, its outer lateral slope being broad, equi- 

 lateral, or gently concave ; the inner slope convex, very narrow, angulated 

 by three radiating ridges, the middle one of which is the strongest. 



The second plate of this range is narrow and sellate, the antero-lateral 

 slopes being concave, and the apex overarching. The posterior portion is 

 angulated, without carina, and is broadly curved, making a moderately sharp 

 ""- 1 '' with the antero-lateral faces. This plate is nearly bi-laterally symmet- 



