ECHINODERMS FROM GREENLAND CLARK 429 



as the shortest peripheral. The great variation iii the size of the 

 paxillae gives the abactinal surface a curious appearance. The 

 spines on the inferomarginal phites are up to 4.5 mm. in length. 



In the second specimen from locality IX (E. 5849) there are 

 10 rays; K=50 mm., r=20 mm. This specimen resembles the preced- 

 ing. In the central portion of the abactinal surface tlie plates, larger 

 and smaller, are more or less evenly spaced over the surface, no 

 reticulate arrangement being discernible, and the paxillae are mainly 

 of two sizes, large and intermediate, most of them the latter. On the 

 outer half of the disk and on the arms there is a regidar very open 

 reticulation of narrovv- bands with isolated and scattered small plates 

 in the interstices. Here the paxillae are m.ore definitely differen- 

 tiated into larger and much smaller, the latter on the bands between 

 the larger and on the isolated plates in the interspaces. 



In the specimen from locality XII (E. 5851) there are 10 rays, 

 one of them only half grown; E,= 16 mm., r=T mm. The abactinal 

 skeleton is reticulate with large interspaces, which become larger on 

 the arms. Within these interspaces are rounded isolated plates of 

 various sizes, usually one or two, sometimes a few more, in an inter- 

 space. When small these plates are merely rounded calcareous 

 nodules; when larger they bear according to size one to six long 

 slender spines resembling those of the paxillae but shorter and 

 slenderer. The paxillae bear 7-20 (most commonly 10-15) long 

 slender spines of which the central five are much longer and stouter 

 than the peripheral and are serrate in the outer half; the large 

 central spines intergrade with the very short and slender peripheral. 



In the specimen from locality XXIV (E. 5702) (see pi. 58) there 

 are 11 rather slender rays; R = GO mm., r=25 mm. The abactinal 

 skeleton is composed of a great number of small plates of various 

 sizes, evenly rounded or with broadly rounded angles, that are con- 

 tinguous or more or less strongly overlapping, forming an almost 

 complete investment. On the disk there is no suggestion of a recticu- 

 late arrangement, but on the rays the plates tend to group themselves 

 in a close-meshed reticulation with four to six smaller plates radiat- 

 ing from the periphery of the larger paxilla-bearing plates. Along 

 the sides of the arms there is a tendency for the plates to become 

 arranged in irregular transverse bands, paxilla-bearing plates being 

 connected by single plates without paxillae. The smaller plates grad- 

 ually become less numerous, and in the outer portion of the arms 

 only evenly distributed, almost or quite contiguous, paxilla-bearing 

 plates remain. The larger plates on the abactinal surface bear 

 paxillae consisting of a high rounded boss bearing 5-10 (usually 7-9) 

 long spines 1.7 mm. in length. These spines are commonly subequal, 

 but a few of the peripheral may be shorter than the central. Some 



