446 THE CEINOIDEA CAMERATA OF NORTH AMERICA. 



Loboci-iims, from the typical form of which it differs in having a diminu- 

 tive anal tube, which occasionally is reduced to a mere opening from the 

 tegmen, similar to that of Dort/crinus. It departs from Batocrinus in the 

 same character, and in being distinctly lobed between the rays, the plates 

 forming the arm bases are separated by interbrachials, and the arm openings 

 are directed upwards ; in all of which it agrees with Lobocrinus. 



MACROCRINUS W. and Sp. (nov. gen.). 

 (MttKpos long, Kpivov a lily.) 



Calyx biturbinate or subovoid, the plates in part elevated. It may be 

 pointed out as a structural peculiarity of this genus, that the radials, anal 

 plate, and first interbrachials are generally nodose, but the higher brachials 

 and interbrachials almost flat and devoid of all markings. 



Basals rather large, forming a subcylindrical cup. Radials frequently 

 larger than both costals together. Costals quadrangular and pentangular. 

 The number of distichals variable. Arm-bearing plates in contact laterally, 

 except at the posterior side, where they are separated by a small interbrachial 

 plate. Arm openings directed outward. Eespiratory pores in five pairs, 

 placed interradially. Arms from twelve to sixteen, long, subcylindrical ; 

 tips incurving and sometimes flattened, but without increasing in width. 

 Regular interbrachials not numerous ; the anal plate generally supporting 

 two rows of three plates, and a small piece within the arm regions. Ventral 

 disk sliorter than the dorsal cup, composed of comparatively few large plates. 

 Anal opening at the end of an unusually long tube, reaching far beyond the 

 tips of the arms ; it is almost central, straight, stout at the base, but grad- 

 ually tapers upwards so as to be quite slender at the end. 



Distribution. — So far as known restricted to America, and found only 

 in the Upper and Lower Burlington beds, and in the lower part of the 

 Keokuk group. 



Ti/i)e of the genus : Macrocrinus KonincM (Shumard). 



Remarks. — The species for which we propose this genus have been 

 referred successively to Actinocrinus, Batocrinus, and Eretmocrimis, but, as 

 generally admitted, without agreeing with either one of them. They dif- 

 fer from Batocrinus in the more elongate form of the calj'x, the less number 

 and greater length of the arms, and in having but five pairs of respiratory 

 pores ; and from Eretmocrimis in the arm structure, and in having a long, 

 straiffht, and almost central anal tube. 



