SINUITES ANCEPS. 5 



Perner ^ and Bassler^ have employed this generic name. Unfortunately the 

 species B. hilohatus has been made to comprise a somewhat miscellaneous assort- 

 ment of forms, and the customary usage of the specific name has become loose 

 and unsatisfactory, as the author^ pointed out in 190G. 



The chief criteria of the various species included in this genus lie in the shape 

 of the transverse section of the whorl, the height of the umbilicus, the internal 

 thickenings of the shell, and the outline of the apertural lobes and shape of the 

 dorsal sinus. The expression " apertural curve " is used below to indicate the 

 curve described by the lateral margin of the mouth (= apertural lobe) in relation 

 to a straight line let fall vertically through the umbilicus from the l)ase of the 

 dorsal sinus. The external ornamentation would be more often useful as a 

 distinguishing specific feature if more generally preserved. 



1. Sinuites anceps (Salter, MS.). Plate I, figs. 1 — 3. 



1878. Bellerophon hilohatus, Sowerby, var. anceps, Salter, MS., Catalogue of Cambrian aucl Silurian 

 Fossils in the Museum of Practical Geology, Jermyu Street, p. 57. 



Specific Characters. — Shell somewhat compressed laterally, outer whorl em- 

 bracing all the inner whorls ; umbilicus closed, minute, subcentral, situated 

 at rather less than half height of shell. Outer whorl gradually increasing in 

 height to mouth, with early part of whorl rounded and subparabolic in section 

 and very faintly trilobed, but becoming subrhomboidal in section towards mouth ; 

 sides steep, gently convex below, but excavated above, so as to meet the 

 dorsum at right angles ; dorsum becoming increasingly flattened and elevated 

 towards mouth, broad, with sharp, subrectangular lateral edges. Mouth sub- 

 rhomboidal, with lateral lobes large, angulated (?) and projecting, and with a 

 deep U-shaped sinus occupying the whole flattened dorsum. Surface of shell 

 marked with fine, gently sigmoidal transverse striae curving back concentric to 

 sinus on dorsum, and with a few stronger transverse ridges. Traces of weak, 

 narrow, internal thickenings crossing sides and dorsum. 



Horizon. — Middle Bala Beds (Soudley Sandstone). 



Locality. — Horderley ; Soudley Quarry, Craven Arms. 



Dimensions. — Height, about 23 mm. Thickness at umbilicus, about 12 mm. 



Eemarhs. — The original specimen [28025] named by Salter is in the Jermyn 

 Street Museum. There is some variation in the degree of globosity of the shell 

 and in the excavation of the sides, for in another specimen [28027] (from the 

 same locality) in Jermyn Street these features are more pronounced than in the 



1 Perner, op. cit., p. 69. 



= Bassler, 'Bibliogr. Index Amer. Ordov. Silur. Foss.' (Bull. 92, U.S. Nat. Mus. 1916), vol. i, 

 p. 1159. 



» Reed, ' Geol. Mag.' [5], vol. 3, 1906, p. 364. 



