286 Dr. P. H. Carpenter on the 



can make good this omission he has no right to speak of my 

 proposal of any new genus as " arbitrary and without any 

 good reason." 



I shall await his reply with interest, as I have utterly 

 failed to discover the passage to which he alludes. When- 

 ever I have been led to establish a new genus I have 

 invariably supplemented the diagnosis of its characters by a 

 further exposition of its " essential points of structure " or of 

 " the most important morphological differences " between it 

 and preexisting genera; and in no one case is there any 

 allusion of this nature to the minor details which are men- 

 tioned by Mr. Hambach. They are frequently of value for 

 specific discrimination, though quite useless so far as genera 

 are concerned. 



Going back for a moment to the classificatory value of the 

 " composition " of the exoskeletal plates, I have sometimes 

 thought it possible that Mr. Hambach's use of the word may 

 be explained by the following passage * : — " Now, if we 

 consider the second point, i. e. the external openings, the so- 

 called spiracles, we will find that Mr. Carpenter is very 

 inconsequent in his argument ; for he says, ' Mere differences 

 in the relative sizes of the calyx-plates are of very little 

 systematic value,' etc. But, it seems, Mr. Carpenter forgets 

 that the differences in the external openings are caused by 

 the very differences in the relative sizes of the deltoid and 

 lancet pieces." 



In reply to this, I can only say (1) that I do not understand 

 how any one who has even glanced at my account of the 

 structure of the spiracles in Schizoblastus, Granatocrinus, and 

 Troostocrinus respectively f can speak of my having for- 

 gotten the share which the deltoids and lancet pieces take in 

 their formation. (2) The relative sizes \ of these plates have 

 nothing to do with the differences in the structure of the 

 spiracles. In Granatocrinus derbiensis almost the whole of 

 the body is formed by the deltoids, as the radials are only 

 just sufficiently high to enclose within their sinuses the distal 

 ends of the ambulacra. On the other hand G. Norwoodi 

 possesses very large radial plates, extending from the edge of 

 the hollow base almost to the very apex of the calyx, and 

 correspondingly small deltoids. The size and general relations 

 of the lancet piece are the same in both types ; and although 

 the deltoids differ so much in relative size, yet Mr. Hambach 



* Trans. St. Louis Acad. Sci. vol. iv. p. 544. 



t Ami. & Mag. Nat. Hist. ser. 5, vol. ix. April 1882, pp. 238, 244- 

 246, 248. 



X If Mr. Hambach would substitute the word "shape" for "size" I 

 sbould be disposed to agree with him. 



