THE 



GEOLOGICAL MAGAZINE, 



NEW SERIES. DECADE V. VOL. IX. 



No. IX.— SEPTEMBER. 1912. 



Sedgwick Muskum JS'otes. 



I. — Notes on the Genus Tsinucleus. — Part IL 



By F. E. COWPER Eeed, M.A., F.G.S. 



(PLATE XIX.) 



(Concluded from the August Number, p. 353.) 



5. Cmnpcirison of Tipper and Loiver Surfaces of Head-shield. 



AS above stated, the arrangement of the pits on the lower surface of 

 the fringe is not invariably the same as that on the upper surface, 

 and we may now examine the degree of correspondence or difference 

 iu the better-known British species. 



In T. fimbriatus'^ there is only a single row of pits close to the 

 margin on the outer band of the lower surface, and they lie below 

 the radial grooves on the upper plate, but they correspond with the 

 outermost row of pits in these sulci only. The upper surface has all 

 the pits arranged in radial sulci (except near the genal angles where 

 the sulci die out), and of these 5-6 rows of pits the outermost is the 

 largest, the others being very shallow, but increasing in size at the 

 genal angles. The lower surface has an inner band, which bears fine 

 radial sulci corresponding in number to the pits of the marginal row 

 and each holding 3-4 small pits ; towards the genal angles the pits do 

 not lie in sulci. These sulci and pits have no corresponding structures 

 on the upper surface (PI. XIX, Figs. 2, 2a). 



In T. hibernims'^ there are no definite radial sulci on the outer band 

 of the lower surface, but the pits in the rows are radially arranged and 

 more or less fused in front, though at the sides they become quite 

 separated and isolated in two distinct rows. These two rows corre- 

 spond with the second and third rows on the upper surface, which has 

 three rows of pits in front fused into short deep radial sulci ; laterally 

 these radial sulci only show two pits, and these approach one another 

 more and more towards the genal angles till at last they fuse into one. 

 The inner band of the lower surface has a single row of large pits 

 corresponding in number to those of the outer band, but not represented 

 at all on the upper surface (PI. XIX, Figs. 1, la). 



These two species show, therefore, very considerable differences in the 

 pits of the upper and lower surfaces of the fringe. 



■^ Salter, in Murchison's Silur. Syst., p. 660, pi. xxiii, fig. 2 ; McCoy, Syu. 

 Pal. Foss. Woodw. Mus., p. 146, pi. iE, fig. 16. 



2 Eeed, Geol. Mag., Dec. IV, Vol. II, p. 52, PI. Ill, Figs. 2-7, 1895. 



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