On the Structure o/" Crotalocrinus, 897 



Issel. Two other species [Pholas dactylus, L., and Solen 

 vaijina, L.) had reached Ismailia. One could wish it were 

 not so proverbially difficult to prove a negative ; for, if Mactra 

 olorina and Mytilus variabilis did not exist at Port Said, or 

 in anj part of the Mediterranean, prior to the opening of the 

 Suez Canal (and in the total absence of evidence the other 

 way, one may fairly assume this to have been the case), their 

 passage from one sea to the other in the short space of 

 thirteen years is an event remarkable in the history of distri- 

 bution. It will be interesting, too, to notice whether the 

 species in question have undergone, or are undergoing varia- 

 tions as a result of their change of locality. 



XXXIX. — Note on the Structure of Crotalocrinus. By P. 

 Herbert Carpenter, D.Sc, F.R.S., F.L.S., Assistant 

 Master at Eton College. 



The third part of Messrs. Wachsmuth and Springer's " Re- 

 vision of the Palteocrinoidea," the second section of which 

 has recently appeared*, contains the following statement 

 respecting the suborder " Articulata," which, as defined by 

 the authors, includes the family Ichthyocrinidie, together with 

 the three genera Crotalocrinus , Enallocrinusj and Cleio- 

 crinus : — 



" We maintain, however, that the outer test of the ventral side 

 in this group was a continuous integument, composed of calcareous 

 plates, united by ligament and not by a close suture, and that by 

 reason of this structure and the articulation among the plates of the 



dorsal side it must have been pliant or flexible That there 



was an inner integument roofed in and covered by the flexible vault 

 wc have mentioned, and that it contained the summit-plates and 

 ' covering pieces,' we know to be true in the Crotalocrinidae, and 

 we think it altogether probable that the general plan of the ventral 

 structure for the Articidata generally is expressed in that of Crotalo- 

 crinus.'^ 



This last paragraph contains a somewhat positive and em- 

 phatic statement. The authors " know it to be true " that 

 Crotalocrinus had a flexible vault above the summit-plates, 

 which, be it remembered, themselves covered in the disk on 

 which the peristome and ambulacra were situated. It has 

 generally been considered hitherto that the summit-plates of 



* Proc. Acad. Nat. Sci. Philad., March 30, 1886, p. 64. _ The paging 

 of the separate copy is 140, and in future references the pagination of the 

 entire work will be quoted, not that of the Philadelphia " Proceedings." 



