DESCRIPTIONS OP THE si MX' IKS. L59 



1 have enumerated eighteen specimens of this species .... On another still smaller 

 piece of nuk are twenty-one specimens . . . On a third fragment of rock thirty may 

 be counted, and on a fourth upwards of fifty" l . 



In the ambulacra of P. God 'oni the lateral grooves are not q U j te at r igHt angles to 



the main groove, but are inclined very slightly downwards. The outer ends 

 of these depressions can hardly be called sockets, like those described by the late 

 Mr. Billings in /'. pyriformtS, but each of them is simply a fine tailing off of the 

 groove. Both the pores and the sockets at the ends of the short grooves proceeding 

 from them appear to be more or less of a pyriform shape. Billings described five 

 hydrospire folds on each side of an ambulacrum in /'. Godoni, whilst Roemer figured 

 four, five, and six respectively. We have seen four and five, hut four appears to be 

 the more common number (PI. II. fig. 13; PI. XVI. fig. 19). 



We have been much perplexed as to the limits of this species, but we have examined 

 a very large number of specimens and the result has been that six, or perhaps seven. 

 varieties have been distinguished. We have endeavoured to illustrate these gradations 

 by a series of outline drawings of the natural size (PI. II. figs. 1-7). They are : — 



1. Large elongated variety approaching P. Burlingtonensis, M. & W., in its 

 general outline (i=Mitra rugoso, quinque perforata, Cumberland). (PI. II. fig- 1.) 



2. Ordinary ovoid form, with the bodies of the radials more or less at right angles 

 to the vertical axis. This may be termed the species proper. (PI. II. fig. 3.) 



3. Calyx sharper and longer than the preceding, with the bodies of the radials 

 much more inclined to the vertical axis. (PI. II. fig. 2.) 



4. Calyx shorter and more expanded, subtruncate below, (=P. abbreiiatns, Ham- 

 bach). (PI. II. fig. 4.) 



5. Calyx similar, but with the bodies of the radials very oblique to the longer axis. 

 (PI. II. fig. 6.) 



6. Calyx squat and expanded, almost truncate below, and the ambulacra much 

 bent down. (PL II. fig. 5.) 



7. Calyx small and almost globular, with wide and deeply petaloid ambulacra. 

 (PL II. fig. 7.) 



By the kindness of Mr. Wachsmuth we are also enabled to figure an extremely 

 young condition of this species wdiich is about the size of a small pea (PL XVI. 

 figs. 22, 23). Its characters are sufficiently evident from our figures, which render 

 further remarks unnecessary. 



We are also indebted to him for the opportunity of examining the various mal- 

 formations of the calyx which are figured on PL II. figs. S-12, and described on 

 pp. 40, 41. 



It does not appear to have been generally noticed that Troost 2 , in describing I'. 

 Godoni, considered Pentrcmitcs ellipMcus, G. B. Sby., as a synonym of it ! 



1 Joura. Acad. Nat. Sci. Philad. 1825, vol. iv. pt. 2, p. 2'Jo. 



2 Trans. Geol. Soc. l'ennsylv. 1S:C>, vol. i. pt. 2, p. 229. 



