REPORT ON" THE CRINOIDEA. 211 



ambulacral skeleton of the pinnules, though well-developed as compared with that of 

 species which have no covering plates at all, is far less highly differentiated than in 

 Antedon jiexilis and in Antedon spinifera itself, which have more distinct side plates 

 than many species of Pentacrinidaa. It is worth notice that with the single exception of 

 Antedon denticulata from 49 fathoms, no member of the Basicurva-gcoup was obtained 

 by the Challenger from a less depth than 140 fathoms, while they range as far down- 

 wards as 1600 fathoms. The bidistichate species with the same characters of the rays 

 and ambulacra range from 80 to 740 fathoms, so far as is yet known ; and the tridistichate 

 species, which also have flattened rays and plated ambulacra, are likewise almost 

 exclusively limited to the continental and abyssal regions. These facts are of interest 

 because the Pentacrinida?, which also have an ambulacral skeleton on the pinnules, do 

 not occur at depths of less than 70 fathoms and range down into the abyssal fauna ; 

 and we may therefore not unreasonably infer that fossfl species like Millericrinus pratti, 

 which have the ambulacral skeleton still preserved on the pinnules, lived at depths of at 

 least 50 fathoms. The same conclusion may perhaps be drawn for those Comatulse such 

 as Solanocrinns costatus, Goldfuss, in which the axillary radials and the lower brachials 

 are very distinctly flattened and wall-sided. 



The following key to the Spinifera-growp contains the names of four Caribbean species, 

 two of which, Antedon brevipinna and Antedon spinifera, have been described by 

 Pourtales and myself respectively. 1 Antedon duplex is one of the hosts of the encysting 

 Myzostoma murrayi, von Graff, which also occurs on Antedon breviradia and Antedon 

 angustiradia of the Challenger collection, both species from the Eastern Archipelago. 

 Antedon pourtalesi is a fine species which I have dedicated to the memory of the late 

 Count Pourtales, and is the host of Myzostoma brevipes, von Graff. 



6. The Spinifera-grovq)). 



Bidistichate species with the radial axillaries and some of the following joints more 



or less wall-sided, and a well-marked ambulacral skeleton on the pinnules : — 



A. Over thirty cirrus-joints ; the later ones spiny. 



I. The first pinnule much smaller than the second. Centro-dorsal a thick 

 disk or low rounded column, bearing two or three tiers of cirrus- 

 sockets usually without definite arrangement ; .eighty or ninety 



cirrus-joints. First radials completely visible, . . . 1. macronema, Mull, sp. 



II. The first pinnule as long as or longer than the second. 



a. Centro-dorsal shortly columnar, with five double rows of cirrus- 

 sockets, separated by interradial ridges. 



1. Twenty arms of sharply carinate joints; eighty ciirus- 



joints or more, . . . . . .2. quinquecostata, n. sp. 



2. Thirty arms, their joints bearing curved dorsal spines ; 



forty to sixty cirrus-joints, .... spinifera, Carpenter. 



1 Bull. Mus. Comp. Zool., 1867, vol. i. No. 6, p. Ill ; Ibid., 1881, vol. ix. No. 4, p. 8. 



