216 



ECHINODERMATA— PELMATOZOA 



PHYLUM IV 



Family 8, Crotalocrinidae Angelin (emend. Wachsm. and Springer), 



Dicydic. Infrahasals five. Calyx resembling that of Cyathocrinus, hut with 

 lower brachials more or less rigidly incorporated into dorsal cup by lateral contact 

 among themselves, with the radials, and with tegmen plates. Tegmen composed of 

 numerous rigid plates, chiefly modified ambulacrals and interambulacrals, with orals 

 more or less exposed, and alternating covering plates often very definitely arranged. 

 No interradials except at anal side. No radianal ; anal x in line with radials ; 

 anus directly through the tegmen or at the end of a short protuberance. Arms non- 

 uniserial. Axial canal in arms distind. Stem large, round. Silurian. 



The systematic position of this family is uncertain. The usual rigid incorporation of the 

 lower brachials in the dorsal cup by inclusion within the radial facet, and by eonnection 

 with solid tegmen, analogous to what is seen in camerate genora like Marsipocrinus and 

 Pterotocrinus, points to a eonnection with the Camerata, as claimed by Wachsmuth and 

 Springer. This feature is subject to considerable Variation, being usually not so pronounced 

 in young specimens, in which the brachials are more nearly isolated. On the other band the 

 resemblance in habitus of calyx to the Inadunata, as Bather has suggested, is equally 

 striking ; while the absence of pinnules in the arms seems to this reviser a strong reason 

 in favour of Inadunate affinities, The structure of the tegmen would place it close to the 

 Cyathocrinidae. 



Enallocrinus d'Orb. Infrabasals five. Anal plate one, not always 

 truncating the posterior basal. Radial facets wide and shallow, bearing 



Fig. 313. 

 A, Crotalocrlnv.ii pulcTier Hising. {Anfhocrinus loveni Müller). Silurian ; Gotland. Crown with folded arms. 

 7>, Portion" of stem. C, Cross-section of four contiguous arm-ossicles of the network. D, Dorsal aspect of 

 arm-plates, showing their intimate union ; those above the two rows ttgured have been broken away so as to 

 expose the side-pieces and covering plates of the ambnlacral furrows. E, Tegmen of C. rugosus Miller (after 

 Angelin). 



directly on their distal edge a triangulär primibrach and one to three further 

 Orders of brachials at each side. Arms long, frequently dichotomising, and 

 becoming free above the first few brachials. Silurian ; Gotland, England. 



Crotalocrinus Austin (Anthocrinus Müller) (Fig. 313). Similar to Enallo- 

 crinus, but arm-branches united by lateral processes from each brachial. 



