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446 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
Lobocrinus, 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 Dorycrinus. 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 Lodocrinus. 
MACROCRINUS W. and Sp. (nov. gen.). 
(Maxpés long, xpivov 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. Respiratory 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 shorter 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. 
Type of the genus: Macrocrinus Konincki (Shumard). 
Kemarks. —The species for which we propose this genus have been 
referred successively to Actinocrinus, Batocrinus, and Eretmocrinus, but, as 
generally admitted, without agreeing with either one of them. They dif- 
fer trom Batoerinus in the more elongate form of the calyx, the less number 
and greater length of the arms, and in having but five pairs of respiratory 
pores; and from Hretmocrinus in the arm structure, and in having a long, 
straight, and almost central anal tube. 
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