210 DISCOVERY REPORTS 



The superficial portion of the mouth-plates slopes downward from the outer end to 

 the broad actinostomial margin, which is close to peristomial membrane and carries 

 6-8 skin-covered spines to each pair of plates. The median, longest, of the fan are about 

 as long as the median suture and slightly shorter than the pair of suboral spines, which 

 stand on the distal margin and are in all respects like the first adambulacral spines. The 

 median marginal spines carry a few to a conspicuous tuft of pedicellariae ; the laterals 

 have a few or none. These lateral members of each comb overlap those of the adjacent 

 "jaws" and close the narrow entrance to the ambulacral furrow. 



The madreporite is on the extreme margin of disk and difficult to find in large al- 

 coholic specimens owing to crowding of the swollen genital region of ray. In young 

 specimens it has a single groove (interradial in direction) and resembles a miniature 

 "bivalve". This groove next becomes sinuous (R 47 mm.). 



Pedicellariae. The pedicellariae are all very small. Those which thickly cover the 

 surface of the sacculi measure, in adults, o- 11 5-0- 14 mm., measured on the long axis of 

 the figures (Fig. G, 5-56). The first to be developed are on the terminal sacculus of ray 

 (stage 2 under " Development") ; next (stage 4) they appear on the primary radial plate 

 and a very few on the adambulacral spines. The first of the lateral sacculi of the ray 

 probably do not develop until after the young leave the brood chamber. All these 

 pedicellariae are essentially similar in shape and size. When the animal is practically 

 adult the larger and differently formed pedicellariae of the marginal mouth spines appear 

 on slight flanges of tissue. These measure o- 16-0-185 mm. high. The base of each blade 

 or jaw is greatly developed and flares outward as may be appreciated from the figures 

 (Fig G, 6a, 6b). The middle piece (mp) is very large, while the excessively fine teeth of 

 centre of jaw are much more numerous than in the common type of pedicellaria. It is 

 probable that the oral pedicellariae, appearing as they do rather late, will be more 

 valuable as a generic character than the other type, which resemble, in a general way, the 

 small pedicellariae of Odinia, Brisingaster, and even those of the distantly related 

 Brimingella and Freyellaster. 



Gonads. The gonads when ripe are voluminous and form two clusters to each ray, 

 almost filling the genital chamber at its base. The ovary opens on distal margin of 

 the first intercostal area at about mid-height of the second skeletal arch ; while the male 

 gonopore is in the centre of the area. 



NiDAMENTAL CAVITY. In each interradius or axilla, so that the interradial angle 

 (with its 2 first skeletal arches) forms part of its walls, is the cavity where eggs are 

 deposited and develop. The very concave intercostal area i forms either side wall ; while 

 interdigitating spines of arches II and III and of the dorsal plates, above area i, con- 

 stitute a sort of basket work, with small passages through which water can circulate. The 

 manner in which these dorsolateral spines interlock is evident from the photographs, but 

 what is not clearly shown is that some of the spines form a continuous organic bridge 

 between adjacent rays. These sharp spines, either by their growth or by the expansion of 

 the body wall deeply pierce the integument of the opposite ray, and the sheath of the 

 spine coalesces with the skin of the opposite ray. When the rays are forced apart the 



