482 



ATELECRINUS. 



the centrodorsal. First radials more arched, oblong, and quite free laterally, their breadth in the 

 adult being one and a half times their length. Axillarics pentagonal, sometimes twice the length 

 of the second radials, into which they have a slight backward projection. Their width is about 

 equal to their length, but their proportions and also those of the second radials vary slightly in 

 different individuals. 



"First brachials well separated laterally, with their inner sides shorter than the more rounded 

 outer ones. 



"Second brachials irregularly quadrate, projecting slightly backwards into the first. The fol- 

 lowing joints have oblique ends and markedly unequal sides. Except in the syzygial joints, the 

 length is at first less than the breadth, but gradually becomes more equal, and exceeds it after the 



fifteenth joint. Terminal joints rela- 

 tively longer and more equal sided. 

 Arm bases smooth, but the middle 

 and later joints overlap slightly. 



"The first syzygium in the third 

 brachial. The following syzygies at 

 intervals of from one to six, usually 

 of two or three joints. 



"First pinnule nearly always on 

 the twelfth brachial, and consisting 

 of about a dozen elongated joints. 

 The following ones increase in size 

 and in the number of joints, de- 

 creasing again towards the arm ends. 

 The lower joints of the middle and 

 later pinnules bear irregular spinous 

 processes on their dorsal edges. 



"Mouth somewhat eccentric and 

 surrounded by a large peristome. 

 A little way behind this is the anal 

 tube, which is also slightly eccentric 

 in position. Disk 6mm. in diame- 

 ter. In the " Challenger ' ' specimen a 

 very few minute calcareous granules 

 are visible on its ventral surface, and 

 also on its sides between the rays. 

 The "Blake" specimens are more 

 naked. The brachial ambulacra lie 

 close down upon and between the 

 muscular bundles, and have a few 

 scattered sacculi at their sides. Color 

 of skeleton white or brownish white." 

 "The distinctive characters of 

 Atelecrinus balanoides are: (1) the 

 transversely oblong shape of the second radials, which are but slightly incised to receive the bluntly 

 angular proximal edges of the axillaries; and (2) the outline of the lower part of the calyx, 

 which slopes uniformly downwards from the radials on to the centrodorsal, without the basal 

 being specially prominent at the interradial angles as they are in Atelecrinus cubensis." 



"The nine individuals of Atelecrinus which I have examined, all agree very well in their gen- 

 eral characters, but differ considerably in the relative proportions of the two outer radials and of 

 the lowest brachials respectively. In all of them which have enough of the arms preserved, the 

 first pinnule is on the twelfth brachial, except in one arm of one individual, in which the tenth 

 joint bears the first pinnule." 



Fig. 15. A. balanoides P. H. Carp, (nach Carpenter, 1. c, 

 1881, pi. 1): a Seitenansicht des Calyx eines anderen 

 " Blake"-Exemplares als des auf unserer Tafel 6, Figur 5, 

 dargestellten X 8; b, b'. Ein einzelnes Basale (ohne seine 

 centralen Fortsatze), b von der Aussenseite, b' von oben X 

 14; c Radialia und Basalia von unten; die kleinen Fort- 

 satze an den Ccntralenden der Basalia sind fortgelassen 

 X 10; d das Centrodorsale von oben X 10. 



Ueber das Centrodorsale schreibt Carpenter 1881, 1. c, p. 67: 



"The acorn shaped centrodorsal of Atelecrinus balanoides is nearly aa deep as high. The 

 opening of its cavity has a narrow pentagonal rim, from the interradial angles of which strong 

 ridges descend the sloping walls, diminishing in size as they approach the apex, where they die 



