MUSEUM OF COMPARATIVE ZOOLOGY. 273 



the lower surface, resembling, in fact, the anal groove of Echinobrissus, and 

 allied genera with inverted position. The actinal system is elliptical in the 

 trend of the groove, very large, with sharply defined edges covered by very 

 minute plates. There are no indications of a floscelle. The odd ambulacrum 

 carries lar^e, thick tentacles, with a slightly lobed disk, while the tentacles 

 of the other ambulacra are peculiar. They are placed, one for each plate, far 

 apart, branching at the extremity, strengthened by a rod separating in the 

 three branches, each terminating by a well-marked disk. There is no peta- 

 loid portion in the ambulacra ; they are all simple pores from the mouth to 

 the apical system. The spines are long, curved at the base, as in Spatan- 

 goids, but the tubercles to which they are attached have not a sunken, 

 scrobicular area. The mamelon is small, crenulated, perforate, surrounded 

 by a large granulated, scrobicular area, and raised above the surface of the 

 test, to which the milled ring is attached by a very flexible muscular mem- 

 brane. There are smaller spines of a similar structure scattered irregularly 

 over the test, but quite distant. The whole appearance of the test is bare, 

 and it is only on the ridges along the anterior groove, round the mouth and 

 anus, that the small spines are closely packed together. Ridiating from 

 the apex towards the mouth, and extending along the abactinal plastron, 

 there are masses of pigment cells forming lines of dark violet spots, also a 

 similar series of spots round the extremity of the anal prolongation of the 

 test, particularly marked on the edge of the pit leading to the anal open- 

 ing. From the above description it is evident that Infulaster and the 

 Ananchytidae must have had a structure allied to that of Pourtalesia, and 

 are embryonic Spatangoids, still retaining some features of Clypeastroids, 

 while the features characteristic of young Spatangoids are prominently 

 developed. 



Off the Tortugas in 349 fathoms. 



Lissonotus fragilis A. Ac, nov. gen. et sp. 



This genus has the general outline of Maretia, but is somewhat more 

 elongate. It must, from the description of Grube, be closely allied to 

 Platybrissus, but the presence of a subanal fasciole, as well as a slight an- 

 terior groove, readily distinguish the two genera, in addition to the presence 

 of a rudimentary rosette in Platybrissus, wanting in this genus. The mouth 

 is not labiate, but pentagonal, with a well-developed floscelle, while the re- 

 maining portion of the ambulacra, extending to the apical system, are simple 

 pores, one for each ambulacral plate, so that the ambulacral areas, seen 

 from above, are scarcely perceptible, marked only by the somewhat more 

 closely packed minute tubercles covering the ambulacral plates. Seen in 

 profile, the test is regularly arched anteriorly, from the lower side to 'the 

 apex, running then almost horizontally, and abruptly bevelled at the pos- 

 35 



