THE EDR1OASTEROIDEA 



211 



stretched two thinly plated membranes, rarely preserved. The dorsal 



membrane contains irregular non-imbricating plates (Miller & Faber, 



1892). The plates of the ventral membrane (apud J. Hall, 1866) were 



delicately reticulate, and arranged in 



numerous rays passing from a central 



pyramid of minute plates [mouth ?]. 



Eccentrically, between two rays, is an 



oval opening [anus ?]. Outside the 



frame is a border of smaller plates 



as in Agelacrinus. The animal was 



not permanently sessile [but could 



probably fix itself like a limpet]. 



As- 



Cijclocystoides Sulti-ri. ,4s, supposed 

 region of anus ; mm, frame of larger mar- 

 ginals. The plated aspect of the flooring, 

 is based on 

 ise the figure 

 pied 



The classificatory position here 

 assigned to the Edrioasteroidea 

 is not that usually accepted by 

 zoologists, although many have F UJ . vm. 



given them equal, nearly equal, 

 or greater classificatory value 

 under various names (see heading, seen through the openi 



,,,, Miller & Faber; othei-wb 



p. 205). Whatever may eventu- copied from Hail, x >.=. 

 ally prove to be the value of the 



characters insisted on in the present work or in others, even if 

 there be traced a closer connection with Diploporita than is as yet 

 apparent, the Edrioasteroidea can never be thought a less distinct 

 or less homogeneous group than, say, the Blastoidea. The zoologi- 

 cal importance of the Edrioasteroidea is another reason for raising 

 them to this position. Many zoologists, e.g. Forbes, Billings, Neu- 

 mayr, Steinmann, have regarded them as connecting either the 

 Echinoidea or the Asteroidea with the Cystidea. On the hypothesis, 

 ever becoming more probable, that all eleutherozoic Echinoderms 

 are descended from some pelmatozoic ancestor or ancestors, then 

 the Edrioasteroidea are alone among Pelmatozoa in presenting a 

 type of ambulacrum from which the holothurian, stellerid, and 

 echinoid types may readily be derived. 



LITERATURE OF PELMATOZOA. 



1. Agassiz, A. 1892. (Calamocrinus Diomcdac . . . with notes on the apical 



system and the homologies of Echinoderms.) Mem. Mus. Comp. Zool. 

 Harvard, vol. xvii., No. 2, 95 pp., xxxii. pis. 



2. Angelin, N. P. 1878. Iconographia Crinoideorum in Stratis Sueciae 



Siluricis Fossilium, 4to, iv. and 62 pp. , xxix. pis. Holmiae. 



3. Austin, T. and T. 1843. (Descriptions of several new genera and species of 



urinoidea.) Ann. Mag. Nat. Hist. (1) vol. xi. pp. 195-207. (Palaeo- 

 zoic Crinoids and Blastoids.) 



4. 1843-1849. Monograph on recent and fossil Crinoidea, 4to, 128 pp., 



xvi. pis., London and Bristol. 



