146 



] 



ECHINODERMATA. 



No. 447. [938, Cast]. Mariacrinus nobilissimus, Hall. 



This species, constituting the type of this genus, is one of the largest and 

 finest known Crinoids in the Silurian system. It bears a general resemblance 

 to Olyptocrinus ; but it has four basal plates, three pentagonal and one hexa- 

 gonal. The column is round, consisting of joints, gradually growing thinner 

 towards the body. A remarkable feature is that the main arms give origin to 

 armlets or fingers which bear the tentacles. This magnificent specimen of a 

 nearly entire individual is from the Lower Helderberg (Upper Silurian, Litch- 

 field, N. Y. 



No. 448. Melocrinus (Ctenocrinus) typus, Bronn. 



This genus is peculiar to the Devonian. Lower Devonian, Eifel, Prussia. 



No. 449. [945, Cast]. Pentacrinus (Extracrinus) Briareus, Miller. 



Size, 2 ft. 2 in. x 1 ft. 10 in. 



The Extracrinoids of Aus- 

 tin are Pentacrinoids with 

 unequal radial plates. The 

 majority of the individuals 

 found are much distorted, 

 and their arms tangled and 

 broken by the action of the 

 waves before they were 

 buriedinthemud. This slab, 

 containing a multitude of 

 beautifully preserved bodies, 

 is from the Lias of Whitby, 

 England, and is now in the 

 Ward Collection, University 

 of Rochester. 



No. 450. Pentacrinus Briareus, Miller. 



A smaller specimen of this beautiful crinoid from Lyme-Regis, England. 



No. 451. Pentacrinites cingulatus, Munst. 



Stems. The columns of this genus are five-sided, and the articulating facets 

 of the joints are marked by crenated ridges, making a pentapetalous figure. 

 The column is provided with " side-arms." Oolite, Boellert, Wurtemberg. 



No. 452. 



[942, Cast]. Pentacrinus subangularis, Miller. 



Body and stem, on slab. This genus of five-sided Crinoids, 

 is still represented by a few species in the deeper waters. 

 The number of plates or ossicles in a single skeleton has been 

 computed at 100,000. The body-plates are firmly articulated 

 together; the rays of the disc are fixed immediately to the 

 summit of the column by special ossicles; and the stem is 

 composed of angular pieces, generally pentagonal. The arms 

 are very long, and thickly beset with side-arms and minute 

 pinnae. This specimen, of unusual size and perfection, is 

 from the Lias, Boll, Wurtemberg. 



Size, 4 ft. 5 in. X 1 ft. 6 m. 



