HAMBACH STRUCTURE & CLASSIFICATION OF PENTREMITES. 545 



Diagrams to show connections of deltoid pieces and ambulacral fields : By a and b, is the 

 covering integument removed to show the sutures between (a) deltoid and (b) lancet 

 pieces; A, Pentremites sttlcatus •, B, P. melo \ C, P. Norvtoodi. 



enough, so as to surround these openings fully, hence they have 

 to remain sepai^ate, or, in other words, where we have ten dis- 

 tinctly visible openings (see Fig. 5, b). This division would em- 

 brace species as 



Pentremites melo Owen iS: Shumard, 



" Sayi Shumard, 



" Roemeri Shumard, 



" Burlingtoncnsis, Meek & Worthen, 



" cretitilatus Roemer, 



and others. 



The third division would comprise all those species in which 

 the deltoid pieces are perforated (see Fig. 5, c), because the lan- 

 cet pieces do not reach far enough to the summit to enter into 

 the composition of the spiracle openings. This division would 

 embrace species as 



Pe7ttremites Nor-woodi Owen & Shumard, 



" Derbiensts Sowerbj, 



" ellipticus Sowerby, 



and others. 



The circumstance of having the deltoid pieces perforated may 

 make it desirable to separate this division from the genus Pen- 

 tremites^ but then the name Granatocrinus ought not to be 

 chosen, as has been done by some of our American writers and 

 now repeated by Mr. Carpenter, as it will confuse matters rather 

 than make them more clear. The type specimen for which Dr. 

 Troost proposed the generic name Granatocrinus^ is Granatocri- 

 nus cidariformis Troost = Pentremites granulatus Roemer. 

 But this species differs very materially from P. Norwoodii Owen 

 & Shumard, as it possesses no perforated deltoid pieces (the chief 



