PART 5 A MONOGRAPH OF THE EXISTESTG CRINOIDS 827 



trapezoidal. According to Carpenter, the pinnules after the lowest increase in size, 

 decreasing again toward the arm tips. The lower segments of the middle and later 

 pinnules bear irregular spinous processes on their dorsal edges. 



Notes. — Hartlaub remarked that Carpenter's figure of Atelecrinus balanoides (1881, 

 fig. 1) gave a too diagrammatic representation of the centrodorsal. The horseshoe- 

 shaped rims about the cirrus sockets are scarcely so well marked, while the distal ends 

 of these rims stand up in a much sharper and more spinelike manner than is shown. 

 The sides of the centrodorsal, which appear as almost smooth, are in reahty markedly 

 imeven and more as they appear in Carpenter's figure of Atf.lecrinus cubensis (1881, 

 fig. 7). The cirrus sockets have a strong central excavation bounded by a prominent 

 horseshoe-shaped rim, and this is outwardly bordered by a narrow oblique surface 

 which is covered by the base of the cirrus. On Carpenter's figure 1 the bases of the 

 cirri appear to be surrounded by the horseshoe-shaped rims, which in reahty is not the 

 case. The basal cirrus segment is very broad in comparison with the 3 short following 

 segments and is not circular in section but laterally compressed and oval. The basals 

 are only visible interradially, and in this respect Carpenter's figure is incorrect. In 

 no case can there be found radially any separation between the radials and the 

 centrodorsal, all traces of an original separation having entirely disappeared. In the 

 specimen from Blake station 260 also, which is only half as large, the basals are not 

 nearly so widely visible as in Carpenter's figure 3, being at the most only perceptible as 

 a very narrow line. There is always a sharp division between the centrodorsal and the 

 lowest calyx plates. The radials are markedly longer than is shown by Carpenter. 



This last statement also holds for the smallest of the specimens examined by 

 Hartlaub (from station 151) which is about half as large as that from Grenada (station 

 260). In it the basals have about the relations shown by Carpenter. 



The surface of the centrodorsal in the specimen from Grenada is somewhat less 

 spiny than it is iu the others. 



Gislen (1928) has given some details of the occurrence and form of the syzygies. 

 Proximally they occur at intervals of usually two muscular articulations, that is be- 

 tween brachials 3+4, 6 + 7, 9+10, and 12 + 13, and distally at intervals of four or five 

 muscular articulations. The syzygies themselves are without muscular fossae; there 

 are 11 to 12 syzj^gial septa in the dorsal half of the ossicles, which are rather distinct 

 and 7 to 8 of them are complete. There is a large deep excavation around the lumen. 

 In the other articulations the muscular fossae are very high. There is no reversion 

 of the proximal brachials and the distal brachials are long and slender, over twice as 

 long as broad. 



The Challenger specimen of balanoides (fig. 53) has the centrodorsal 4.1 mm. Ln 

 vertical height and 3.2 mm. in basal diameter. Even at this size the basals still form 

 a complete, though very narrow, ring separating the centrodoraal from the radials. 

 The short suture between adjacent basals is very hard to see. 



Localities. — Albatross station 2415; off Fernandina, northern Florida (lat. 30°44'00" 

 N., long. 79°26'00" W.); 804 meters; temperature 7.56° C; coral, coarse sand, shells, 

 and foraminifera; April 1, 1885 (1, U.S.N.M., 34956). 



Blake station 43; south of the Dry Tortugas, Florida Gat. 24°08'00" N., long. 

 82°51'00" W.); 620 meters; temperature 7.22° C; 1877-78 [Pourtal6s, 1879; P. H. 

 Carpenter, 1881, 1882, 1888] (1, M.C.Z., 233). 



556-622—67 54 



