Description of Grinoids from the Upper Suhcarhoniferous. 329 



brachials, and subdivided as follows, the subdivisions being on the 

 same side as in the preceding species; the first pair, to the right of the 

 az3'gous area, gives rise to 6, three for each arm: the second pair to the 

 right, also gives rise to 6, three for each arm; the first pair to the 

 left of the azygous area is divided in the same manner; in the second 

 pair there is usually the same arrangement, but in one case the 

 following anomaly occurs: the right area gives rise to two branches, 

 which have no further division: the left gives rise to three, two of 

 which are again subdivided, giving rise to 6 at the free extremity. 

 The pair opposite the az^'gous area is again divided, giving rise to 

 four arms; we thus have, in several cases, 30 arms at the free 

 extremities. The plates upon which these divisions take place are in 

 no case spinous, though thickened and larger than the other plates of 

 the arm series. 



The Azygous Area. — This is similar to that in the species above 

 described, though less prominent. Its connection with the ventral 

 sac, and relation to other internal parts have not 3'et been made out. 



The Ventral Sac. — This is similar in form to that of the previously 

 described species, except that it is divided longitudinally into a 

 series of grooves separated by acute ridges, within which grooves the 

 arms or pinnulse are folded ; this feature of the organ is indistinctly 

 shown in the upper part of fig. 8, at the left, where the extremity of 

 the sac may be seen just beneath the edges of the dome plates. The 

 roof of this organ may consist of five spine-bearing plates, as seen in 

 fig. 9, which represents the top of fig. 8, or of 7 plates, as in other 

 specimens, or of 8, as seen in fig. II ; the latter specimen, however, was 

 found apart from the crinoid to which it belonged. It is plain that 

 the number of spines or of dome plates can not be regarded as a 

 specific character. As may be seen by the figures cited, these spines 

 are very long and slender. . 



The PinnulcB. — These are longer and less stout, accordingly, than in 

 the preceding species, from which this difi'ers in its more elongated 

 habit. 



The Column. — This is pentagonal, and very much resembles that of 

 the preceding species. 



This crinoid may be distinguished from the previous species by its 

 greater size, more slender habit, want of spines on the arm-dividing 

 plates, fluted ventral sac, more rounded and comparatively small body, 

 smaller number of free arms, and by the much smaller number and 

 greater size and thickness of the top plates of the ventral sac, with 

 their greatly elongated spines. Altogether it is one of the most grace- 



