BEFOPT ON THE CBINOFDEA. 241 



value, as there is no tridistichate Antedon of the normal type with a syzygy in the 

 third brachial which has flattened rays and protected ambulacra. 



A still more striking instance of reversion to the more generalised condition is some- 

 times met with both in Antedon angusticalyx and in Antedon insequalis. The tridistichate 

 series may be replaced by a bidistichate one ; but this apparently unimportant variation 

 is always accompanied by a change in the grouping of the syzygies above the distichal 

 axillary. Except in one or two abnormal species like Actinometra pulchelld, the first 

 two brachials are never united by syzygy when they follow two articulated distichals ; 

 and so when a bidistichate series occurs as a variation in Antedon angusticalyx or 

 Antedon insequalis the first two brachials are articulated, and there is a syzygy in the 

 third. This is well seen in the two lateral rays of the figured specimen of Antedon 

 angusticalyx 1 (PL L. fig. 1). 



There is one species of the Granulifera-gcowp which presents a different type of arm- 

 structure from the rest. Antedon porrecta is also tridistichate, but the second joint 

 above the distichal axillary is a syzygial one (PI. LII. fig. 3). There are often no 

 palmars ; but when they do occur the series consists of two joints, the axillary a syzygy, 

 so that the formula of the type becomes A.3.2{(p..)br} . This is the only species of 

 Antedon with a syzygy in the second brachial, though the character is a common one in 

 Actinometra, as seen in PI. LX.; PI. LXII. fig. 3 ; and PI. LXVI. figs. 1, 4. 

 The species of the Granulifera-gTowp may be classified as follows : — 



A. A syzygy between the first two brachials. 



I. Calyx and arm-bases not spinous. The first two pinnules about equal, 

 with compressed and carinate joints ; the genital pinnules have un- 

 equally expanded joints. 



a. Primary arms of adjacent rays in close lateral contact. Palmars 



usually absent ; the second syzygy generally not beyond the 

 fifteenth brachial. 



1. Cirri smooth and without an opposing spine. First radials 



invisible; the second very short and deeply incised. The 



lower joints of the distichal pinnule not specially wide, 1. angusticalyx, n. sp. 



2. Cirri somewhat carinate, with an opposing spine. First 



radials partly visible. The lowest joint of the distichal 



pinnule much wider than the rest, . . .2. inxqualis, n. sp. 



b. The distichal axillaries of adjacent rays partially separated by the 



pinnule of the preceding joint. Palmars usually present ; the 

 second syzygy from the twentieth to the twenty-fifth brachial. 



1. The lower pinnules rather stout, .... .7>'aM"^/era,Pourtales. 



2. The lower pinnules comparatively slender, . . 3. didincta, n. sp. 

 II. Calyx and arm-bases spinous. The first pinnule much longer than the 



second, with stout joints, the lowest of which have their inner edges 



cut away. The genital pinnules have uniformly expanded joints, . 4. multispina, 2 n. sp. 



B. A syzygy in the second brachial, . . . • • .5. porrecta, n. sp. 



1 The fourth brachial is the syzygial joint in one arm of the right-hand ray. 



2 Some forms of this species have only ten arms ; see p. 117. 



(ZOOL. CHALL. EXP. PAKT LX. 1887.) 000 31 



