166 CATALOGUE OF THE BLASTOIDEA. 



such species as P. obesus, Lyon l ; P. robustus, Lyon 2 ; P. cervinus. Hall 3 ; P. basilaris, 

 Hambach 4 , &c. The first of these appears to differ from the present species in the 

 greater length of the calyx, especially of the basal portion, the more acute, longer, and 

 less truncate summit, and the somewhat less curved ambulacra. In P. cervinus the 

 ambulacra expand much more outwards than they do in P. sulcatus, and the depth 

 of the base from the radial lips downwards is greater, giving quite a different appear- 

 ance to the lower part of the calyx. 



According to Prof. Hall 5 , P. Cherokeeus, Troost (MS.), is identical with P. sulcatus. 

 We have no direct means of forming an opinion on this point, for we lack specimens 

 not only of this species but also of many others about which we much desire to 

 satisfy ourselves. We must leave intricate questions of synonymy like this to our 

 American co-workers for solution, as any attempt on our part would be absolutely 

 futile in the absence of the necessary material. We may, however, remark in pass- 

 ing that Hall's figure of P. Cherokeeus exhibits very small deltoid plates projecting 

 above the summit, a feature quite at variance with Roemer's figure of P. sulcatus. 



The number of hydrospire-folds which occur in this species appears to be somewhat 

 variable. In the polished section, which is represented on PI. XVI. fig. 20, five 

 tubes appear on the left side of the ambulacrum and four on the other ; while in the 

 transparent section of the same calyx, which is shown on PL XVIII. fig. 5, there is 

 an indication of a sixth tube on the left side. It is formed as a diverticulum of 

 what appears to be the normal outermost (or fourth) tube of that side, but is evi- 

 dently quite short, as it does not appear in the other section of the same ambulacrum 

 (PL XVI. fig. 20). 



The reduction of the number of hjdrospire-folds at the distal end of the ambu- 

 lacrum, and their enclosure within the radials, as in P. conoideus, is well shown on 

 PL II. fig. 31. (See p. 95.) 



Zittel has figured a section of the hydrospires in a species which he calls Pentre- 

 mitcs sulcatus, Say 6 . We suspect, however, that it is really the P.pyriformis of Say, 

 P. sulcatus being Roemer's species. At any rate his section is much more like that 

 of our P.pyriformis (PL XVIII. fig. 3) than those of P. sulcatus, which have more 

 hollowed ambulacra (PL XVI. fig. 20; PL XVIII. fig. 5), and also deep concavities 

 in the interradial areas of the calyx; and these last are altogether absent in Zittel's 

 figure. 



13 v the kindness of Mr. Charles Wachsmuth we are able to figure a fine specimen 



1 ralccontological Report, Owen's 3rd Report Geol. Survey Kentucky, 1857, p. 469. 



2 Trans. St. Louis Acad. Sci. 1860, vol. i. no. 4, p. 629. 



3 Iowa Geol. Report, 1858, vol. i. pt. 2, p. 090. 



* Trans. St. Louis Acad. Sci. 188u, vol. iv. no. 1, p. 159. 



6 Iowa Geol. Report, 1858, vol. i. pt. 2, p. 691, 



6 Uandb. Pal. 1879, Bd. i. lief. :'•, p. 429, f. 301 b, p. 433, f. 306. 



