BRITISH FOSSILS. 



3 



oblong, and obtuse. Their under surfaces exhibit oblong, rather broad, 

 ambulacral plates, gradually decreasing in size towards the tips of the 

 arms, but nearly equal for about two-thirds of their length. The 

 ambulacral sulcus between them is rather broad. The largest specimen 

 examined measured an inch and a half across. 



Affinities. — The contour of this fossil star-fish strikingly reminds us of 

 that of the living Uraster hispidus, but the structure of its dermal cover- 

 ing was very different. With no fossil as yet discovered can it be 

 confounded. 



Locality and Geological Position. — First found in lower Silurian rocks, 

 at Drumcannon, near Waterford, in 1846, by Sir Henry De la Beche, 

 Captain James, R.E., and the describer ; since by Mr. Gibbs, of the 

 Geological Survey, in Bala rocks, at Moel y Garnedd, near Bala, North 

 Wales. In the Irish locality it was associated with Phacops Jamesii and 

 numerous Orthides. In the Welsh with Orthides., Trilobites of the 

 genera Asaphus and Homalonotus^ and numerous stems of Encrinites. 



Fig. 4. 



URASTER HIRUDO. 



E. Forbes, " Memoirs of the Geological Survey of Great Britain," 

 vol. ii. part 2, p. 464. 



Diagnosis. U. brachiis quinis, linear i-lanceolatis, acuminatis, disco 

 minuto ; pagind superiori reticulata, decussatd (spinis fasciculatis, fasciculis 

 spinarum seriehus longitudinalibus dispositis) ossiculis amhulacralibus ob- 

 longis, ambulacris latis. 



Description. — Body very minute, about a fourth as broad as the rays 

 are long ; rays tapering and linear-lanceolate, contracted at their bases, 

 pointed at their extremities. Their upper surface clothed with bundles 

 of spines arranged in very regular rows, and so placed that each ray 

 seems to be marked by three or four longitudinal furrows, crossed at 

 regular intervals by transverse grooves. Under surface with short 

 ambulacral plates and broad avenues. The largest specimens do not 

 measure more than an inch across. 



Affinities. — Unlike any fossil star-fish with which I am acquainted, 

 and possibly not a member of this genus. 



Locality and Geological Position. — Gregarious in Silurian (Ludlow) 

 rocks at Pottersfell, near Kendal, in Westmoreland ; first found by 

 Mr. John Ruthven, and communicated by Professor Sedgwick. Its 

 aspect reminds us of Ophiura. 



