Morphology of the Blastoidea. 237 



places these two species in the same division of the genus 

 Pentremites, which he describes as follows * : — a The third 

 division would comprise all those species in which the deltoid 

 pieces are perforated, because the lancet pieces do not reach 

 far enough to the summit to enter into the composition of the 

 spiracle openings." 



As the large deltoids of Granatocrinus derbiensis and the 

 small ones of G. Norwoodi are both perforated by the spiracles, 

 Mr. Hambach should tell us what characters of these openings 

 in the two species respectively are due to this very consider- 

 able difference in the relative sizes of the deltoids. But he 

 does not mention them at all ; and they cannot be so impor- 

 tant as he makes out, for he places the two species in the 

 same genus, just as has been done by the older pala3ontologists 

 and by Mr. R. Etheridge, Jun., and myself. 



Although we are in accordance upon this point, I cannot 

 admit the truth of Mr. Hambach's teleological argument as 

 to why the deltoids of Granatocrinus are perforated. But in 

 the absence of proper figures it is useless to discuss this point, 

 about which Mr. Hambach is as positive as if he had personally 

 assisted at the evolution of a Granatocrinus. 



In spite of all his criticism of my views he gives a classifi- 

 cation of the so-called Pentremites which is essentially based 

 upon the structure of the spiracles ; and it therefore corre- 

 sponds somewhat closely with that which has been already 

 proposed by Mr. 11. Etheridge, Jun., and myself f. He 

 says J, li Still, if we suppose such a classification, accor- 

 ding to the differences in the spiracle openings, w r as de- 

 sirable and necessary, we could only (according to their 

 external aspect and arrangement) divide them into three 

 divisions." 



It is not quite clear from the above passage what it is 

 which Mr. Hambach proposes to divide into three divisions, 

 the genus Pentremites^ about which he is supposed to be 

 writing, not having been mentioned since the middle of the 

 previous page. Upon examining the list of species which he 

 gives under each division, however, I find that in No. 1 are 

 included those which Mr. Etheridge and myself refer to Pen- 

 tremites and to Troostocrinus. No. 2 corresponds to our 

 Schizoblastus, together with two species which have puzzled 

 us considerably on account of their somewhat generalized 

 characters ; while No. 3 is identical with Granatocrinus as 

 we understand the genus. It is not a little gratifying to us 



* Trans. St. Louis Acad. vol. iv. p. 545. 



f Ann. & Mag. Nat. Hist. ser. 5, vol. ix. pp. 219-248. 



X Trans. St. Louis Acad. vol. iv. p. 544. 



