THKEE NEW SPECIES OF METACPJNUS. 437 



twenty -two joints more. There is usually a syzygy iu the third joint after each axillary. 

 The next is somewhere hetween the twelfth and thirtieth brachial, and others follow at 

 very irregular intervals. 



The three radial pinnules, on the second, third, and fourth radials, are large and pro- 

 minent, reaching 20 millims. in length, and consisting of 18-20 joints. The three lower 

 ones are massive and cuboidal ; the next few flattened laterally, but still stout, and pro- 

 jecting beyond the bases of their successors. This is most marked in the smaller terminal 

 joints, so that the end of the pinnule lias a very serrate appearance. The first distichal 

 pinnule is much like those on the radials ; but the following ones are smaller and less 

 serrate. The two lower joints are flatteued, and much wider than their successors ; but 

 this inequality is much less marked after the palmar axillary, and disappears altogether 

 in the later pinnules, which are comparatively small. 



The disk is covered by an irregular pavement of small plates, set moderately close, 

 and the ambulacra are well protected by plates; but the perisoine at the sides of the 

 disk, between the rays, is almost bare. 



Neither are the muscular bundles between the arm-joints covered by plates, which are 

 limited to the ambulacra. They form a fairly regular row on each side, and become 

 differentiated at the bases of the pinnules into more or less pointed side-plates and 

 rounded covering-plates. Colour, a very light yellowish brown, which has scarcely 

 altered in spirit. 



Hub. Sagami Bay, Japan ; 70 fathoms. 



Remarks. — Several well defined characters distinguish this fine species from the various 

 types of Metucrinus which were dredged by the ' Challenger.' 



In the first place, like M. Moseleyi, it occupies an intermediate position between the 

 two groups into which most species of the genus very naturally fall : — 1. Those with 

 four radials, of which the second is a syzygy ; and 2. Those with six radials, of which 

 both the second and fourth are syzygies. Variations from these numbers occasionally 

 present themselves in single rays of individual specimens ; but, as a general rule, the 

 presence of four or six joints in a ray is a very constant character. 



This is not the case, however, in 31. Moseleyi, two individuals of which were dredged 

 by the ' Challenger.' The following variations occur among their ten rays : — 



1 ray of three joints, with the second and the axillary a syzygy. 

 i ,, ioiu ,, ,, ,, ,, ,, ,, 



3 rays of five ,, ,, ,, a syzygy. 



2 ,, ,, „ ,, ,, and the fourth a syzygy. 



1 ray of six ,, ,, ,, a syzygy. 



2 rays „ „ n ;) and the fourth a syzygy. 



In the single specimen of M. rotundas the construction of the five rays is as follows : — 



1 ray of six joints, without a syzygy. 



2 rays of five joints, with the second a syzygy. 



1 ray of five joints, with syzygies in the second and fourth. 



1 ray of five joints, with syzygies in the second and axillary. r 



G5 



r.* 



