4.42 DR. P. H. CARPENTER ON 



Metacrinus superbus is somewhat closely allied Loth to 31. Murrayi and to 31. nobilis, 

 having, like them, a smooth flat stem and normally only four radials, and also ahout the 

 same number of joints in the primary and secondary arms. It has slightly shorter inter- 

 nodes than both these types ; and the joints composing them arc less sharply pentagonal 

 than in 31. nobilis, though the sides are not quite so much incurved as in 31. Murrayi. 

 Both the supra- and the intranodal stem-joints are about as mucli incised as in the latter 

 species, and somewhat less so than in 31. nobilis. In neither of these species are there 

 more than about 50 cirrus-joints, and the interarticular pores end at about the tenth or 

 twelfth node; whereas in 31. superbus there are some 65 cirrus-joints, and the inter- 

 articular pores extend down to the eighteenth node — a most unusual distance from the 

 calyx. 



Both these types, again, differ altogether front the larger 31. superbus in the smoothness 

 of the dorsal surface of the skeleton as far as the middle of the free arms; while the 

 terminal portions of their arms are distinctly more serrate than in the corresponding 

 parts of 31. superbus. 



Two of the radial scries are slightly irregular in the specimen now under consideration. 



The type consists of live primitive joints, the second and third of which have united 

 to form a syzygy ; so that I he ultimate number of radials is four, with the second a 

 syzygy. On two rays, however, there were six primitive joints. In the one case the 

 second and third united as in the type, while the rest remained free; so that there are 

 two joints between the syzygy and the axillary, as shown in PI. LI. fig. 1. In the 

 next ray, however, the axillary became united by syzygy to the joint beneath it, and the 

 proximal and distal edges of the hypozygal are raised and thickened, as in the other parts 

 of the ray, but only for rather more than half their width. This is also the case with 

 the proximal edge of the axillary or epizygal, the smaller half of which appeal's as a 

 simple syzygial line, while the remainder is raised and thickened. 



The disk, though mutilated in parts, is very well preserved for a dry specimen, and 

 presents one or two points worth notice. The peristome is large, but has no visible oral 

 opening, and a large number of food-grooves converge upon it, some of which proceed 

 direct from the large lower pinnules, as is always the case in this genus. There is, there- 

 fore, a great number of small interambulacral areas, which are paved by small plates 

 that are pierced by numerous water-pores, but not so closely set as to form a continuous 

 pavement. These perforated plates extend over on to the dorsal side between the ray- 

 divisions, just as they do in Pentacrinus asterius; though Miiller denied their existence in 

 this position *. The skeleton of the pinnule-ambulacra varies somewhat in appearance, 

 according to the size of the pinnule which bears it (PI. LIL figs. 10, 11). The side-plates 

 are usually low and rounded, and very different in appearance from the sharply pointed 

 plates which correspond to them in 31. rotuudus. The gradual development of the 

 pinnule-ambulacra from that of the arm is well shown in PL LI. fig. 2. In this, as 

 in all species of the genus, the ambulacra do not reach the distal ends of the pinnules, 

 but terminate some little way short of them ; and in like manner the terminal portions 



* " Uobcr den Lau des Pentacrinus Caput-Medusm," Abhandl. d. Berlin. Akad. 184:?, p. 49. 



