Yol. 55.] ECHINOIDEA AND OPHITTBOIDEA. 693 



porite is involved in the determination of the ventral aspect of the 

 specimen. 



As regards the structures described as vertebral ossicles, their 

 form is so obscure that additional evidence as to their nature was 

 felt to be necessary, and permission was asked, and very kindly given 

 by Dr. Woodward, to have one of the arms of the fossil sliced across 

 for closer examination. Dr. Gregory was good enough to have this 

 operation carried out. Two arms were traversed by the section ; 

 neither showed any indication of such a structure as had been 

 imagined to represent a vertebral ossicle. One had evidently been 

 broken along the median ventral line after death and crushed so 

 that the broken ends overlapped (an overthrust on a small 

 scale), but it contained no vertebral ossicle ; the second arm had 

 likewise been broken, and some loose plates were scattered in the 

 interior, but it was not possible certainly to identify any of these 

 with a vertebral ossicle, though some might possibly be open to this 

 interpretation. 



A question arises as to the external skeleton of the arms. 

 Dr. Woodward described them as covered by minute imbricated 

 plates, the projecting points of which give it an extremely scabrous 

 appearance. Dr. Gregory states that the arms have no external 

 arm-plates, but are covered by a granular integument : by this, no 

 doubt, he merely intends to express the opinion that the scales 

 covering the arms cannot be correlated with those of recent 

 Ophiuroidea. Transverse sections present no natural apertures by 

 which tube-feet could be extruded to the exterior, and an examina- 

 tion of the surface shows that it was completely covered by closely- 

 arranged overlapping plates, which are of two kinds : one larger, 

 prominently projecting, with thickened conical ends, exhibiting a 

 tendency to become mucronate ; the other smaller, thinner, and less 

 projecting, with gently- rounded terminations. No openings are 

 visible at any point of these heavily-armoured appendages. Dr. 

 Woodward, and subsequently Dr. Gregory, have spoken of these 

 appendages as ' bifurcated ' or ' branched ' arms. It is conceivable 

 that they may be so, but such a view does not seem to be supported 

 by evidence. Avoiding hypothetical terms, the appendages of each ray 

 may be spoken of as a paired series, the members of which are 

 gradually larger from the mouth outwards. There are seven pairs 

 in each series, of which the first or most proximal is situated on the 

 buccal armature, taking its origin from one of the plates of the 

 dental rosette. If the arms were provided with vertebral ossicles, 

 and if these articulated with a series of similar ossicles arranged 

 along a radius, the term ^ bifurcate or branching arms ' might 

 perhaps be appropriate, but there is not the least evidence that this 

 is or ever was the case, though a branching of the nerves and 

 vessels supplying the arms must be conceded. The succeeding 

 pairs pass out from a series of openings on the ventral side of the 

 ' disc,' and there is a separate opening for each appendage, so that 

 on the removal of these bodies a paired series of holes is left in the 

 waUs of the test. 



