330 CAMBRO-SILURIAN FOSSILS. 



thing of the sort in his large species ; and further^ the coarse 

 punctation of Trematis does not exist here. I think its zoolo- 

 gical position very doubtful ; the greatest affinity is probably with 

 Siphonotreta (which it resembles very much if the tube in the 

 beak be viewed as modified into a groove by a cleft or division 

 of the internal rostral pad, the walls of which would thus cor- 

 respond to the cardinal bosses of the present genus, forming a 

 passage thus to Obolus). I think a peculiar family should be 

 formed to include those three genera, the family being placed 

 between Crania and Discina. 



Spondylobolus craniolaris (M'Coy). 



Sp. Char. Suborbicular, depressed, slightly undulated, the width 

 scarcely exceeding the length, front and sides broadly rounded, 

 slightly acuminated behind ; apex near the posterior margin ; 

 substance of the shell thick, calcareous, smooth, with very 

 minute faint concentric strise, very minutely fibrous, but- the 

 punctation (if it exists) indistinct ; beak of small valve small, 

 obtusely pointed at about one-fourth the length from the 

 posterior margin; beneath the beak the shell is greatly 

 thickened, forming an obtuse wide pad, internally reaching 

 nearly to the margins ; beak of larger valve terminal, slightly 

 produced, apparently channelled below by a triangular groove, 

 on each side of the base of which is a strong conical boss, 

 projecting into the cavity of the opposite valve like cardinal 

 teeth ; surface dull, nearly smooth, or showing under very 

 strong glasses an indistinct, very minute punctation (perhaps 

 due to the fibrous tissue of the shell) and delicate concentric 

 strise. Length 4 lines, width 4^ lines. 



The specimens I have examined are chiefly internal impres- 

 sions, showing two very deep small oval pits near the hinge-line, 

 resembhng the so-called Crania Sedgwickii of Davidson (Bull, de 

 la Soc. Geol. de France for October 1848), from which it differs in 

 the greater approximation of these impressions (which are clearly 

 not analogous to the muscular impressions of Crania), smaller 

 size, &c. 



Five or six specimens have occurred in the shale of Builth 

 Bridge, Radnorshire. 



(Col. University of Cambridge.) 



Holopella tenuicincta (M^Coy). 



Sp. Char. Very elongate, spiral angle 20°, whorls probably eight 

 or nine, but only five or six usually preserved, gently convex, 

 sutures simple, deep, sutural angle 80° ; surface girt with close, 



