38 



CATALOGUE OF THE BLASTOIDEA. 



Ophioglypha minuta (Fig. IV. C), and they together represent the deltoids of Eloea- 

 crin us or the single calyx-inter radial of the Bolland Platycrm us. In other Ophiurids, 

 such for example as Ophiomusium granosum and 0. validum, the interradial series 

 starts from a basal, its lowest plate (or plates) separating two radials (Fig. IV. D) ; 



Diagrams to illustrate the structure of the interradial area of the calyx between the actinal 

 and the abactinal systems. 



A. Elmacrinus elegans (modified from Hall). B. Platycrinus, sp. C. Ophioghjpha minuta. 

 D. Ophiomusium validum. (C and D adapted from Lyman.) 



1. Dorsocentral. 2. Under-basals. 3. Basals. 4. Radials. /. Interradials. R.S. Radial 

 Shields. G.S. Genital Scales. 0. Orals. 



and a parallel to this sometimes occurs in abnormal specimens of Blastoids, such, for 

 example, as the Pentremites sulcatus figured by Hambach 1 , in which two of the 

 radials are separated by a long plate which rests on a basal below and supports the 

 deltoid above. 



The posterior deltoid of Elceacrinus is divided into two parts by the anal plate ; 

 and it may be noted that the same sort of arrangement occurs in many of the earlier 

 Palseocrinoids, in which, however, the first anal plate often rests directly on a basal, and 

 not on a radial, as in the Blastoid. Thus, for example, Wachsmuth and Springer a 

 point out that in Glyptaster, Eucrinus, Dorycrinus, &c. "the first true interradial in 

 the posterior area is divided, and is represented by two smaller plates, separated by a 

 special anal plate." In GJyptocrinus, which has a complete radial ring, and also 

 five regular interradials in the first series, there is the same general arrangement of 



1 Trans. St. Louis Acad. Sci. 1880, vol. iv. no. 1, p. 154, pi. B. fig. 11. 



2 ' llevisiou of the ralrcoerinoidca,' part ii. (Proc. Acad. Nat. Sci. Philad. 1881, pt. 2), p. 13. 



