44 MR. F. J. BELL ON A NEW GENUS OF ECHINOIDS. [Feb. 3, 



w as not mentioned or described by the late Dr. Gray in his ' Cata- 

 logue of the Recent Ecbinida,' pubHshed in 1855. It is much worn 

 and has much the a))pearance of a fossil specimen ; in the opinions of 

 Prof. Morris and of Dr. Henry Woodward, F.R.S., however, the spe- 

 cimen is recent. It was bought at Stevens's sale-rooms, and is, with 

 a doubt, reported to have come from India. To the accomplished 

 palaeontologist just named I have to express ray thanks for instructed 

 guidance through the cabinets under his charge ; and while I take 

 on myself all responsibility in describing this form, I would say at 

 once that it is the fact that it was unknown to Dr. Woodward which 

 has chiefly led me to regard it as new. 



As we pass in review the edentulous forms of the Irregular Echi- 

 noidea, we are led irresistibly to the conclusion that the shortening of 

 the ambulacra and the arrangement of the pores in the mode which 

 has led Prof. Hackel to give to the group the name of Petalosticha}, 

 are structural changes whicli have gone hand in hand ; and, just as we 

 may say of the ungulate Mammalia that their limbs tend to become 

 modified by the reduction of the outer digits, and that, where success 

 is attained, this reduction is accompanied by concomitant changes in 

 the relations of the metacarpal or metatarsal bones to the carpus or 

 tarsus', or of the Araneina that they have tended to limit their stig- 

 mata to two^ so may we say of the Petalosticha that the arrangement 

 of the ambulacral pores in straight parallel rows is more ancient than 

 that in which the greater number are set in petaloid fashion. So far 

 the generalization is borne out by the evidence of the palseontological 

 succession, while some of the observations of Alex. Agassiz seem to 

 support it on the embryological side. Perhaps we may go a step 

 further and say, with safety, that the longer, the more regular, and 

 the straighter are, step for step, older arrangements than rows of 

 pores less long, less regular, or less straight. It is obvious that all 

 kinds of stages may be found in tliis series if the regular and orderly 

 modification of the Echinoderm structure has taken place in the non- 

 saltatory fashion which it is now the mode to ascribe to the process 

 of Evolution ; but there is another possible process which it is, after 

 all, not so much more diflficult to present distinctly to the imagination ; 

 and that is progression by leaps of varying breadth ■*. Prof. Agassiz 

 has drawn attention to the sudden transitions which he has observed 

 in the growth of an individual, and to the apparently sudden ap- 

 pearance of genera in their geological succession. Let us test these 

 two conflicting views by the evidence afforded by the new genus ; 

 but before doing so, let us point out that, even if we shall find evidence 

 in favour of the sudden or, as we may call it, saltatory character of 

 the transitions, it is just what we seem to find also in the develop- 

 mental history of the individual; so that it affords us, just as well as 

 any more steady succession, quite as complete a demonstration of the 



1 Gener. Morphologie, ii. p, Ixxiv. 

 " Kowalevsky, Proc. Eoj. Soc. 1873, p. 153. 

 3 Cf. Bertkau, Archiv fiir Naturg. 1878, pp. 351 et seq. 



* In the sense, of course, that the intermediate forms were so rapidly passed 

 over that the chance of their being preserved is practically nil. 



