196 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



lobed. A curious circumstance is that these specimens closely re- 

 semble examples of Pectinaster hylaccvnthus^ with which they were 

 at first confused, the two forms having been taken at the same 

 dredge haul. They are distinct, however, and really belong to dif- 

 ferent genera, although the presence in both of inferomarginal fas- 

 ciculate pedicellariae is misleading. In hylaccmthus the superomar- 

 ginals are more lateral in position, and the spine is nearer the upper 

 edge of the plate. The pedicellariae have blunter, broader jaws, 

 and the actinal intermediate pedicellariae of niasicus are gencially 

 pectinate — that is, on two plates, although subcircular in shape. The 

 papularium of hylacantlius is more swollen, and when examined from 

 the inner side the plates are seen to be more modified, especially in 

 the center of the area, and the area itself shows no sign of being 

 two-lobed. The superficial similarity of the two species is, however, 

 very striking. 



Ludwig's original diagnosis of Cheiraster niasicus is very brief and 

 incomplete — scarcely more than enough to technically fix the name. 

 There are many points about which more information would be de- 

 sirable ; for instance, the dimensions, proportions of marginal plates, 

 and minor details of ornamentation. But since a number of major 

 characters of the present species nearly or quite agree with the diag- 

 nosis of niasicics, I have given Ludwig's name to the Albatross speci- 

 mens. The description was based largel}' on a specimen from Station 

 5447, Lagonoy Gulf, 408 fathoms. 



CHEIRASTER GAZELLAE Studer. 



Plate 50, figs. 1-3 ; plate 51, fig. 1 ; plate 52, fig. 1 ; plate 54, figs. 3, 3a ; plate 56, 



figs. 1, 2. 



Cheiraster gazellae Studee, 1883, p. 129 ; 1884, p. 50, pi. 4, fig. 8, a, &, c. 



The specimens listed below belong to a corner of the genus in 

 which the features relied upon to differentiate species are subject to 

 considerable variation. The species of this section look alike, so 

 that the characters sought to separate them are difficult to handle 

 because they concern minute, or perhaps subtle, points of structure 

 which do not come out well in photographs, and whicli may even 

 escape the notice of a conscientious observer. The specific groups, 

 into which this section of Cheiraster has been divided, must, there- 

 fore, be considered as experiments. They may not stand the test. 



Ludwig (1910, p. 456) states in his key that the enlarged central 

 spinule which occurs on the abactinal plates of several species, nota- 

 bly pilosus, niasicus^ and inops, is lacking in gazellae. He appears 

 not to have examined specimens personally, judging by a list of 

 species, given on page 436, which he had examined for the dorsal 

 nmscle bands. There is no evidence from Studer's figure that the 

 distal abactinal plates lack the small central spinule (such as cliarac- 



