Ilambdch — Revision of the Blastoideae. 25 



grouped in this genus : Pentremites ellipiicus, P. orbicularis, 

 P. derbiensis, P. oblongus, and P. angulatus. 



" These form a very natural group, easily recognizable, and 

 distinguished from the typical species of Pentremites by well 

 marked characters. They are always of an elliptical or sub- 

 globular shape. Thepseudo-ambulacral areas are narrow, with 

 sides subparallel, and extend usually the entire length of the 

 body. The basal pieces are nearly always concave, and gen- 

 erally situated at the bottom of a deep excavation. The 

 tubular lamellae, which, in the interior reach from the ovarial 

 apertures to the base of the pseudo-ambulacral fields, are 

 more simple in structure, being much less convoluted, while 

 the relative position of the ovarial apertures is different. 



" The typical species of the genus Elaeacrinus , viz., Elaea- 

 crinus verneuili, long previous to the publication of Prof. 

 Roemer's description with figures was well known to Ameri- 

 can and also to some European palaeontologists as Olivanites 

 verneuili, under which name it was designated by Prof. G. 

 Troost in his Monograph on North American Crinoidea, which 

 valuable memoir was completed a short time previous to the 

 death of its author, but is not yet published. According 

 therefore to the laws of priority, Roemer's name, Elaeacrinus, 

 proposed in 1852, must be adopted, although it is to be re- 

 gretted that the learned author did not adopt Troost' s generic 

 name in preference to creating a new one. 



" It is possible that the genus JSFucleocrinus, proposed by 

 Conrad in 1842 (Jour. Acad. Nat. Sci., Philad., Yol. VIII., 

 p. 280, PL XV., Fig. 17), may be identical with Elaeacrinus; 

 but the meager and unsatisfactory description of Conrad 

 (' this genus differs from Pentremites, Say, in having only 

 one perforation at top, which is central') does not apply to 

 any of the forms we propose to group in Elaeacrinus.''' 



In 1866 Dr. Shumard adopts the suggestion of Prof. Hall. 

 He says : * — 



" Adopting the suggestion of Prof. Hall, I here include 

 under Granatocrinus (genus proposed by the late Dr. Troost), 



* Transact., Vol. II,, p. 375. 



