1887.] NATURAL SCIENCES OF PHILADELPHIA. 87 



pieces of adjacent ambulacra. The opposite angle toward the centre is 

 acute, and is occupied by a shallow groove which projects in form of a 

 lip toward the center. This form of the oj^ening is remarkably con- 

 stant in all the si^ecimens of this species, and is characteristic not 

 only of the genus Pentremites but also of Pe)itreviltidea. That in 

 Pentremites a considerable portion of the spiracles was closed by 

 plates of some kind, we think quite probable, but the structure was 

 certainly very different from that described by Shumard. 



In 1850, Owen and Shumard ' discovered a peculiar summit struct- 

 ure in Pentremites in a specimen of P. Godoni, which they described 

 as a "conical covering of small plates." In 1858 Shumard^ ob- 

 served a similar structure in P. sidcatus, of which he gave the fol- 

 lowing account. "In this fossil there rises from the center of the 

 summit a little pyramid with five salient and five retreating angles, 

 the salient angles being directly opposite the extremities of the inter- 

 radial pieces, while the retreating angles correspond to the center 

 of the pseudo-ambulacral fields. The base of this little pyramid 

 is joined to the superior edges of the pseudo-ambulacral fields 

 so as to completely roof in the buccal and ovarial apertures. It con- 

 sists of about fifty pieces, arranged in ten series ; the first or exterior 

 ones in each series being of a triangular form, the others elongated 

 quadrilateral. Two series of pieces stand over each ovarial aperture, 

 those of one side uniting Avith their fellows of the opposite side at 

 the salient angles of the pyramid." 



No further attention was paid to this structure until 1884, when 

 Hambach ^ proposed to amend Shumard's description by adding 

 . that this cone-shaped body "consists of little tubes running parallel 

 with each other and roofing in the summit of the calyx in a con- 

 ical shape (])ut not the central opening.) They protude through 

 the same apertures in which the hydrospires terminate ; there are 

 about five of these tubes to each aperture, which seem to correspond 

 witli the plicas of the hydrospiric sac." He concludes that these 

 tubes extend down into the interior of the calyx, and he takes them 

 "to be the ovarian tubes." 



We can confirm Haml)ach's observation as to the existence of 

 elongate pieces having the external appearance of tubes placed side 

 by side, though we do not concur in his inference of a connection 



1 Journ. Acad. Nat. Sci. Phil., Vol. II. Pt. I, p. 65 

 2Trnns. St. Louis Acad. Sci., Vol. I, No. 2, p. 244. 

 1 Trans. St. Louis Acad. Sci. 1884,Vol. II, No. 3, p. 541 



