ECHINODERMATA. - 
647 
nciiiial system is that of Saicnm, hut the position of the anal system is that 
of Hyposalenia. As nothing is known of the spines of either of these genera, 
tins new genus is established on the peculiarity of the abactihal system and 
tlie imbricated buccal membrane, which is covered thickly with plates ar- 
ranged somewhat as they are in Echinocidaris. The primary tubercles of 
the interambulacral area are large, arranged in two vertical rows in the two 
areas; those of the ambulacral area are smaller, and diminish rapidly towards 
the abactiiial pole. Three posterior genital plates much larger than two 
anterior ; the reverse is the case of the ocular plates ; there is a trace of a 
madreporic body on the largest genital plate. Oflf Double Head Shot Key, 
315 fathoms. 
Ccenopedina mhensis, gen. et spec, nov., A. Agassiz, 1. c. p. 256. This is a 
living representative of Ile^nipedina, Wright, as emended by Desor, but dif- 
fers by the peculiar arrangement of the pores, which have a tendency to 
arrange themselves in lateral arcs of three pairs. General outline of test is 
that of Cyphosoma ; its perforate tubercles are not crenulated, are nearly of 
the same size, and there are but two rows, extending from pole to pole. 
Abactinal part of tost is flat ; the actinal opening is Inrgo, spines long, moder- 
ately slout; genital plates heptngonal, carrying five to six small tubercles 
and as many still smaller ones. Ocular plates pentagonal ; ocular pore large, 
surrounded by an arc of small tubercles. Anal system largo ; plates numerous 
and minute. Anus central. Teeth like those of Echinocidaris ; buccal mem- 
brane is strengthened round the mouth, close to the teeth, by ten large per- 
forated plates, occupying nearly the whole membrane, with eight to ten 
smaller ones around these. From 138 to 270 fathoms. 
Echmus lividus. For its development see Metschnikoflf, /. c. p. 42. 
Echinus yracilis, sp. n., A. Agassiz, 1. c. p. 261. Intermediate between E. 
flemingii, Dali, and E. melo, Lam. From 93 to 200 fathoms. 
Podocidaris sculptUy gen. et sp. nov., A. Agassiz, 1. c. p. 258. Has the 
general facies of a j^oiing Echinocidaris, with a depressed abactinal surface as 
in Astropyga, the ambulacra rising in ridges above the surface. The whole 
surface of the test is covered with long-stemmed articulated pedicellariae, 
having each a distinct mamelon for their support, surrounded by a sort of 
scrobicular circle, the base of the pedicellariae forming a ball-and-socket joint 
with the tubercle, while there is a true muscular membrane holding them 
in place, as in true spines. Only four anal plates, as in Echinocidaris ; genital 
and ocular plates with small rudimentary knob-shaped spines. From 138 to 
315 fathoms. 
Genocidaris maculata, gen. et sp. nov., A. Agassiz, 1. c. p. 262. This is the 
living representative of Opechinus. The spines resemble those of Temno- 
plcurus, but are short ; actinal membrane, with the exception of ten small 
circular buccal plates, is bare : a single circular plate, slightly conical, occu- 
pies nearly the whole anal system, with the exception of a small crescent- 
shaped slit, covered by four very small plates. Genital plates large, pen- 
tagonal; genital opening in a deep groove ; ocular plates pentagonal, elon- 
gated horizontally, From 80 to 160 fathoms. 
Trigo7iocidaris alhida, gen. et sp. nov., A. Agassiz, 1. c. p. 263. Allied to Ge- 
nocidaris. The principal tubercles have the same stmctnie ; but, in addition, 
the whole test is covered by a reticulation of ridges similar to those of Podo- 
cidaris, extending from the base of the different tubercles, and uniting them 
