HAMBACH — STRUCTURE A- CLASSIFICATION OF PENTREMITES. 543 



their development for the one in the deltoid pieces, and for the 

 other in the basal plates or pelvis (see Fig. 3). The most essen- 

 tial difference between Echinus and Pentremites is, that the 

 latter is supported by a fixed column, and that all openings are 

 found on the summit and formed by the apical system, whereas 

 the main resemblance with the Crinoidea lies in the column, and, 

 if you will, in the pinnulse ; whereas mouth, ovarian openings( ?), 

 ambulacral field, with its tentacles and general shape, reminds 

 Fis'. 3. one more of Echinus or Astroidea than of 



Crinoidea or Cystoidea. Even the spines of 

 the urchin are apparently not missing ; — for I 

 have a well preserved specimen of Pentre- 

 mites granulatus Roemer = Granatocrinus 

 cidariformis Troost, on which the coarse 

 granules show very distinct sockets for the 

 articulation of spines(?). Should further dis- 

 Pentremitossulcatus, coveries confirm this view, then this species 



showing the dev 

 ment ot the calyx 

 apical system ; h, 

 nal system. The growth 

 of the test is indi 

 by different shades 



Now, a few words about the proposed new classification of 

 Mr. Carpenter. He says, '' the basis of the classification which 

 ■vs^e have been led to adopt, is the morphology of the hydrospires 

 and of their external openings, the so-called spiracles," etc.* 



The general rule which governs the classification of our fossil 

 Echinodermata, is the difference in the number and composition 

 of pieces forming the exoskeleton. But, contrary to this rule, 

 Mr. Carpenter considers the hydrospires as very characteristic 

 and of much systematic value, although I believe he agrees with 

 Billings in considering them respiratory organs. Admitting this 

 view to be a correct one, and considering the difference in the 

 form in which we find them preserved, we have to admit that 

 they belong to the softer and interior organs ; besides, they are 

 so subject to abnormal developments (see Fig. 4) that it would 

 be hard to say which was normal or which abnormal — a condi- 

 tion which has already been observed by Rofe ; and for this, if 

 for no other reason, we have to reject them as not possessing any 

 characteristics of systematic value. 



* Annals and Magazines of Natural History, April, 1882, p. 214. 



me'rof the%awT:T might be removed from the genus Pentre?ni- 

 naUystS' "Lgro'lfth tes ou accouut of its spincs, but for the pres- 

 of the test is indicated ^^^ j^ ^^^^^^ remains with them. 



