THE CRINOIDEA 



'95 



also X., XXIII. 4). FAMILY 3. ANTEDONIDAE. Pinnata in which the 

 patina consists of 5 small BB, not forming a closed circlet, and RR with 

 large high muscle-plates and facet approaching horizontal ; cavity enclosed 

 by RR is minute ; mouth endocyclic ; proximal Br loosely incorporated in 

 cup ; columnals as in Bourgueticrinidae, but usually lost in the adult, ex- 

 cept the proximale and adjoining columnals which fuse with one another 

 and with IBB to form a single ossicle, the " centrodorsal," which bears 

 cirri ; root when present, encrusting. and x present in brephic stage, 

 but not in adult. Sacculi almost always present. (See structural details of 

 Antedon, Figs. IX., XV., XVIII. 2, 3, 4, XIX., XXX., XXXIII., XL VI., 

 XL VII., XLIX. 8, 9, LIV, LV.) Genera Thiolliericrin us, Etallon (1859), 

 Jurassic and Cretaceous of Switzerland, France, and Portugal (Fig.CXVII.) ; 

 scarcely differs from Mesocrinus, except in the reduction of BB and 

 presence of a cirriferous centrodorsal at the top of the fairly stout stem ; 

 our knowledge of this most important form is due to de LorioL The 

 remaining Antedonidae retain the portion of stem below the centrodorsal 

 only in the brephic stage, while their BB further diminish during geo- 

 logical periods, their adcentral portions fusing into a small 10-rayed plate, 



FIG. cxvn. 



Thiolliericrinus. 1, T.fli. 

 cup seen from below, no basals 

 risible (from Brit. Mus. 49222). 

 2, T. Ribeiroi, from the side, 

 showing basals and facets for 

 cirri (reconstructed from de 

 Loriol's figures). CD, centro- 

 dorsal, still bearing facet (Sf) 

 for attachment to stem, x 2 

 diam. 



the " rosette," which lies above the chambered organ, and in some species 

 of Antedon is all that remains of BB. There is also traceable in the arms 

 a gradual attenuation and, in many cases, increase of forking, with a 

 partial or entire loss of calcined covering-plates. Antedon, de Fremin- 

 ville (1811 ; synn. Alecto, Leach ; Comatula, Lamarck, pars ; Hibernula, 

 Fleming ; Phytocrinus, de Blainville ; Solanocrinus, Goldfuss ; Hyponome, 

 Loven ; Geocoma, Fraas non d'Orb. ; et alia), Lias to Recent, almost all seas, 

 littoral to 2900 fathoms. Arms fork once or more ; Amb usually present, 

 especially on pinnules. The genus is divisible into 9 groups, differing in 

 arm-structure and distribution. Eudiocrinus, P. H. Carp. (1882 ; syn. 

 Ophiocrinus, Semper non Salter), Neocomian (?) to Recent, Pacific and B. of 

 Biscay, 50 to 900 fathoms ; differs from Antedon only in non-forking of 

 arms. Promachocrinus, P. H. Carp. (1879), Pacific and South Sea, 70 to 

 1800 fathoms; 10 RR, probably a persistent meristic variation from 

 more than one species of Antedon. FAMILY 4. ATELECRINIDAE. Pin- 

 nata with patina of 5 BB forming closed circlet and no rosette, 5 RR 

 with high muscle-plates ; arms fork once, IIBr long, with no pinnules 

 on first 8 or 16 ; no stem, but acorn -shaped centrodorsal, with cirri 

 alternating in 5 vertical double rows ; sacculi present. Genus 

 Atelecrinus, P. H. Carp. (1881), Cretaceous (?) to Recent, tropical Atlantic 



