226 Cincinnati Society of Natural History. 



last whorl, extends nearly half the distance from the periphery to the 

 columella. The suture is sharp and distinct, and close up under the 

 keel above. Aperture unknown. The last volution appears to have 

 expanded below for the aperture, but enough is not preserved for defi- 

 nition. 



Surface ornamented by numerous distinct round- striae or lines, ex- 

 tending from the sutures a little obliquely backward to the periphery 

 of the angular keel. These striae increase in width toward the keel, 

 and in two instances on our specimen there is an increase by implan- 

 tation. 



The peculiar keel or flange, and the surface ornamentation, will dis- 

 tinguish this species from any hitherto described. 



It was collected by W. C. Egan, at Bridgeport, Chicago, in the mag- 

 nesian limestone of the age of the Niagara Group, and by him pre- 

 sented to the author. Instead of being a cast of the interior of a shell, 

 as is usual in such limestoue, it is a cast of the exterior of the shell, 

 and is, therefore, remarkable and unique. The specific name is in 

 honor of A. H. Worthen, the distinguished State Geologist of Illinois. 



POTERIOCRINUS DAVIS ANUS, n. Sp. 



[ Plate IX., fig. 4, natural size j fig. 4a, enlarged view of the calyx and brachials ; fig. 45, 

 enlarged view of the azygos side of another specimen ; fig. 4c, an enlarged view of a 

 fragment of an arm.] 



This species is rather below the medium size, the calyx truncated 

 obconoidal, the arms strong, and the column fairly proportioned to the 

 size of the body. 



Column. — The column is long, round, smooth, or with very slightly 

 projecting plates, and very gently expanding to unite with the calyx. 

 The plates are of nearl}- uniform thickness, and where the column is 

 weathered, the serrated union of the plates discloses the radiations 

 upon their uniting faces. 



Body. — The length and breadth of the calyx are nearlj- equal ; the 

 plates are smooth, and the sutures moderately distinct. The basal 

 plates are pentagonal, slightly wider than high, the two upper sloping 

 sides are the shorter ones, and the side articulating with the column 

 has about the same length as the uniting sides between the basals. 

 The subradials are about as wide as high, and quite regularly hex- 

 agonal, except the two on the azygous side, which support the plates at 

 the base of the proboscis, which are heptagonal. The first radial s are 

 pentagonal, three of them wider than long, and the other two about as 

 long as wide. The upper or articulating surface is truncated the en- 

 tire width of the plate, for the support of the brachials. 



