112 



FOSSIL OOLITIC ASTERIAD^E. 



Genus— TLVMASTER, WriglL 1861. 



Rays numerous, long, and plume-like ; narrow at the base, expanded in tlie middle, 

 and tapering gently towards an obtuse apex. Tlie inter-ambulacral ossicula are mucli 

 elongated transversely, they have a row of spiniferous tubercles on the middle of their under 

 side, and their outer distal margin is pectinated fig. 1 h. ; the tubercles carry long hair-like 

 spines, the ambulacral ossicula are thick and prominent, like the vertebral bones of 

 Ophiuriadce ; the avenues are narrow and depressed. The radial bones, at the base of 

 the rays, form a conspicuous prominent ring around the mouth opening (fig. 1 c). 



A. — Sjjecies from the Lias. 



Plumaster ophiuroides, Wright. PI. V, figs. 1 1 b. 



Rays twelve, three times as long as the diameter of the disc, bent, and plume-like ; 

 narrow at the base, expanded in the middle, with obtuse terminations ; ambulacra narrow 

 and depressed, forming a furrow in the centre of the ray ; lateral ossicula long, bent, and 

 slightly arched, with a row of tubercles on the centre of each bone. The proximal side of 

 the ossicula, in relation to the disc, is slightly convex, and the distal side pectinated on 

 its outer half, (fig. 1 b). The rows of tubercles support long spines which lie in situ in the 

 specimen. The radial bones around the disc circle are very prominent, and resemble 

 ancient trusses with a sculptured surface (fig. 1 c). 



Affinities and differences. — This Star-fish resembles Luidia in the general form of the 

 rays, whilst it differs from that genus in the structure of the lateral ossicles, and the possession 

 of a conspicuous row of tubercles along the centre of each bone. It has some resemblance 

 to Fteraster, but the fringe of marginal spines which forms so remarkable a character in 

 Pteraster is wanting in Plumaster. These characters may be said to be generic, rather 

 than specific, and as the specimen under consideration is a unicum, little more can be 

 positively stated on the subject. 



Locality and Stratigraphical jjosition. — This beautiful Star-fish was found by Mr. Peter 

 Cullen in the shales of the Middle Lias near Skinningrave Bay, on the Yorkshire coast ; 

 many of the rays are well preserved, the anatomical details however are partly concealed by 

 an irremoveable pyritic film. This unique specimen is the property of my friend, John 

 Leckenby, Esq., F.G.S., and forms one of the many rarities contained in his rich cabinet 

 of Yorkshire fossils. 



