78 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
primary spines on the flanks of the test. The actinal side of the test is flatter 
than in P. laguncula and the proboscis runs at a less angle from the plane of 
that surface. The color of the test is pinkish ; the radioles are white. 
Station No. 3411, between Bindloe and Wenham Islands, in 1189 fathoms. | 
a “ 3431, off Altata, Gulf of California, in 995 fathoms. 
PLEXECHINUS, A. Ac. 
Only two specimens of this interesting genus were collected. This genus is 
peculiar as combining some of the features of Urechinus and Pourtalesia. Tt 
has the flush actinostome of the former genus, and at the apex the widely sepa- 
rated bivium and trivium of Pourtalesia, with simple ambulacral pores, a slightly 
developed anal proboscis, a sunken anal system, and a well developed broad 
subanal fasciole. 
Plexechinus cinctus A. Aa. 
Plate VIII. Figs. 3, 4. | 
Seen in profile, the test slopes very gradually from the bivium towards the 
rounded anterior extremity. The posterior end is truncated, deeply scooped 
out above the broad anal proboscis for the reception of the anal system. The 
anal proboscis is rounded, curved back anteriorly, and is gradually lost in the 
keel of the actinal plastron. The anal proboscis is banded by a wide fasciole, 
extending far beyond the posterior edge of the anal system to the keel of the 
actinal plastron. On the actinal side the posterior ambulacral areas are broad 
and bare. At the anterior extremity towards the ambitus the test is closely 
covered by primary tubercles; they become smaller as they pass beyond the 
ambitus and cover the abactinal area, and are quite regularly scattered over the 
test with somewhat distant minute miliaries in the intertubercular spaces, 
The anal system is transversely elliptical, strengthened by eight large trape- 
zoidal plates surrounding the central anal opening. 
Station No. 3424, off Tres Marias, Gulf of California, in 676 fathoms. 
Echinocrepis setigera A. Ac. 
Plate XIII. 
Although a number of fragments of this species were collected, only a single 
fairly complete specimen was obtained from Station 3399. It meastured 99 mm. 
in length, 51 mm. in greatest width, and 53 mm. in height. The test was of 
chocolate color; the primary spines from 20 to 22 mm. long were pinkish, 
This species is at once distinguished from E. euneata by the great elongation 
of the odd interambulacrum and the more rounded outline of the test, which is 
far less angular than that of E. cuneata (Challenger Echini, Plate XX VIT. Figs. 
1-5). The anterior ambulacral groove is but slightly depressed above the 
ambitus; the actinal pouch is entirely on the oral surface, and the anterior ex- 
