1890.] NATURAL SCIENCES OF PHILADELPHIA. 359 



were discharged by the tube. This is further probable, if it is true 

 that the ventral tube is the greatly extended posterior area of the 

 ventral disk, and that the " madreporite" represents not the proxi- 

 mal plate of that area but the distal one. The first row of iuter- 

 radials of the posterior side in all Crinoids in which there is either 

 a ventral sac or proboscis, rests upon the special anal plate, if such 

 is present, and hence this cannot be located in a Cyathoerwus at the 

 ventral side of the calyx, but must be looked for at the base of the 

 tube facing the dorsal cup. This, it seems to us, ])roves concki- 

 sively that the perforated plate is a true anambulacral plate, analo- 

 gous with the perforated limestone particles at the disk of recent 

 Crinoids, and not a first interradial. Neither can we regard the two 

 narrow pieces at either side of the " madreporite" as true interradials, 

 i'ov if they represented, as inight be supposed, the posterior interradial 

 split into two halves by the madreporite, they should rest like the 

 middle one against the anal plate. They are strictly subambuhi- 

 cral, supporting one-half of the two posterior ambulacra, the other 

 half resting upon the incurved lateral margins of the adjoining lar- 

 ger plates. This seems to suggest that not only the two smaller 

 plates but possibly also the four larger ones, wholly or in part, are 

 subambulacral plates, and this is not so improbable as it might 

 seem at first sight, if we remember that these parts in all Cyatho- 

 crinidae, perhaps with the exception of Euspirocrinus spiralis, are 

 covered by other structures. 



We have stated before that the " consolidating plates" of Cyatho- 

 crinus were regarded by us and Dr. Carpenter as closely similar to, 

 if not homologous with, the deltoids of the Blastoidea. In both these 

 groups the plates are laterally connected, and partly covered by the 

 ambulacra so as to be in part subambulacral ; but, while in the 

 Cyathocrinidac generally the middle or deltoid j^art is concealed by 

 perisome, it is more or less exposed in the Blastoids. The similar- 

 ity that exists in the structure of these plates between the two groups 

 is best observed by a comparison with Pentremites. In this genus, 

 the deltoid part is heavy, and differs quite distinctly from the con- 

 cealed subambulacral portions, which are comparatively delicate. 



Pentremites has also an interambulacral integument of small 

 plates overlying the upper portions of the deltoids, which either are 

 spinous themselves or covered with spines,' and we cannot help think- 



^ The Summt Plates in Blastoids, Crinoids and Cystids, and their Morpho- 

 logical Relations, by Charles Wachsmuth and Frank Springer (Proc. Acad. Nat. 

 Sci. Phila., 1887. pi^. 9 to 11). 



