190 



ECHINODERMATA PELMATOZOA 



SUB-KINGDOM III 



Norwoodi and in Cryptocrinus melo, the summit is paved by numerous, very 

 minute, irregularly arranged pieces. In the genus Pentremites, as observed in 

 five or six species, the summit is surmounted by a pyramid formed of five 

 elongate, tapering spines, the outermost of which are shorter than the rest. 

 This pyramid not only conceals the summit-opening, but also extends over 

 the greater part of the spiracles and the anal aperture ; , but it leaves at 



FIG. 313. 



A, GranMocrinus Norwoodi, O. and S. Upper face of perfect specimen, with mouth and anus (a) closed by 

 plates. Spiracles (sp) separate. B, Orophocrinus stelliformis, O. and S. Upper face with closed peristome and 

 exposed anus. Spiraoles slit-like. C, Pentremites sulcatus, Roem. Central mouth-opening surrounded by five 

 spiracles, the posterior one confluent with the anus. D, Cryptoblastus melo, O. and S. sp. Upper face with 

 central mouth-opening, large anus, and eight spiracles (after Carpenter). 



the median line of each ambulacrum a channel communicating with the 



peristome.] 



The summit in most Blastoids is surrounded by a cycle of five pairs of 



openings ; and between the two posterior ones there is usually interposed 



a single additional aperture. 

 The former were regarded by 

 Roemer as connected with the 

 genital system, and were 

 called by him "ovarian aper- 

 tures"-, but they are now 

 known as the spiracles. The 

 other opening which pierces 

 the upper end of the posterior 

 deltoid is the anus. 



The form and arrange- 

 ment of the spiracles is ex- 

 FlG 314 tremely variable ; they may 



A, Pentremites Godoni, Defr. sp. Upper face with ambulacral be round Or slit-like ; they 



f pn cpnnrni-P 



fields in various states of preservation, a, Ambulacrum after the ^aw nrmoi ' t 



removal of lancet- and side-plates ; hydrospires exposed ; b, Lancet- mav ( 



plate with upper surface denuded by weathering ; c, Perfectly pre- openings, Or those of the Same 



served lancet-plate bordered by side-plates ; d, The same, but with . , - -, 



transverse markings of lancet-plate obliterated ; e, Ambulacrum pair may be Confluent With One 



covered with pinnules (after Roemer). B, Phaenoschisma aculum, - 1 i ,r 



Sow. sp. Upper face, enlarged ; a, Ambulacrum after removal of another ; and tile posterior 



the lancet- and side-plates; hydrospire slits (hy) cutting through r,oj r T^OTT V> P fns-prl both with 



radials and deltoids ; b, c, Ambulacra in which lancet-plates (Q only P air ma y D<3 1USe . C 



are preserved ; d, e, Ambulacra intact ; lancet-plate concealed, by each Other and with the anUS 



side-plates (after Etheridge and Carpenter). . -i i , i nr.-t 



in which case the fifth or 



posterior spiracle is considerably larger than the others. Granatocrinus, 

 Pentremites, Pentremitidea, etc. (Fig. 314, A), are examples of the latter case; 

 Granatocrinus having five circular orifices with tube-like projections, while in 

 Pentremites and Pentremitidea the four smaller spiracles are divided into two 

 compartments by the terminal median ridge of the deltoids. The posterior 



