TRBMATONOTUS DTLATATUS. 81 



1884. Bellerophon dilatatus, Sowerby, J. D. La Touche, Handbook to the Geology of Shropshire, p. 7£, 



pi. xiv, figs. 489—491. 

 ? 1884. Tremanotus longitudinalis, Lindstrora, Silur. Gastrop. Pterop. Gotland, p. 86, pi. iv, 



figs. 1-7. 

 1892. Trematonotus britannicus, E. B. Newton, Geol. Mag. [3], vol. ix, p. 337, pi. ix. 

 Nnn 1843. Bellerophon dilatatus, Sowerby, var., Portloclc, Geol. Eep. Londond., p. 398, pi. xxix, fig. 1. 

 Non 1852. Bellerophon dilatatus, McCoy, Syu. Brit. Palseoz. Poss. Woodw. Mus., fasc. ii, p. 309. 

 Nov. 1860. Bellerophon dilatatus, Sowerby, Eichwald, Leth. Ross., vol. i, Anc. Per., p. 1067. 



Specific Characters. — Shell discoidal ; whorls few, transverse, about twice as 

 wide as high, slightly overlapping, slowly increasing in size to mouth. Umbilicus 

 open, rather deep, more than half the diameter of the shell ; umbilical edges 

 rounded. Outer whorl with gently convex dorsum becoming more convex and even 

 subangular towards mouth, with a narrow median ridge developed in the distal two- 

 thirds showing along it a few large oval foramina set at subequal distances apart. 

 Mouth large, subtriangular or cordate, higher than wide, with rather abruptly 

 reflexed, much expanded flattened margins, having the upper lip vertical and 

 about twice as wide as the lower lip, and the lateral lips gradually decreasing in 

 width to the lower lip, which descends owing to its reflection as low as centre of 

 umbilicus and is interrupted medially by the inner part of the outer whorl. Small 

 dorsal emargination in upper lip. Exterior of shell ornamented with rather closely- 

 set thick revolving slightly sinuous lines parallel to central ridge but diverging 

 slightly on expanded margins of mouth, and with a few transverse growth-lines. 

 Interior of mouth with expanded margins showing similar thick revolving lines 

 concentrically striated and diverging outwards in a pinnate fashion on each side 

 of the median line of the upper lip. 



Dimensions : 



i ii 



(6712) (4597) 



Height of shell with oral expansion . c. 95 mm. . c. 105 mm. 

 Height of shell to base of mouth . c. 38 ,, . c. 40 ,, 



Width of mouth . . . . . c. 05 „ . c. 75 ,, 



Width of outer whorl at base of mouth c. 20 ,, . c. 23 „ 



Horizons. — (1) Wenlock Limestone ; (1 a) Wenlock Shale; (2) Lower Ludlow?; 

 (2 a) Woolhope Beds. 



Localities. — (1) Burrington, near Ludlow; (1 a) Dudley; (2) Kingsland ; 

 ? Mary Knoll, Ludlow; (2a) Worcester Railway, Malvern [28075]. 



Remarks. — There are two excellent specimens in the Jermyn Street Museum, 

 of which Sowerby's original type from Burrington [6712] (Sowerby, op. cit., pi. 

 xii, tig. 23) is rather less perfect than the other [4597], the locality of which is 

 doubtful. Sowerby's description is as follows : "Discoid, smooth; sides largely 

 umbilicated ; margin broad, slightly convex, with a central ridge ; whorls few ; 

 aperture suddenly dilated to a much greater diameter than the spire and enclosing 



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