SANGUINOLITES STRIATO-LAMELLOSUS. 39^ 



Specific Characters. — Shell of medium size, very inequilateral, compressed, 

 obliquely carinate, transversely rliomb-ovate, its dorso-ventral diameter increasing 

 gradually towards tlie posterior end. The anterior end is short, compressed, 

 elliptically rounded, narrowed from above downwards, excavated above by a 

 narrow elongate lunule. The inferior border is transverse, very nearly straight. 

 The posterior border is obliquely bitruncate, divided into two almost equal por- 

 tions by a well-marked angular projection, each part being slightly concave. The 

 postero-superior angle is obtuse and well marked, and the postero-inferior angle, 

 only slightly rounded, is somewhat less than a right angle. The hinge-line is 

 arched in front, straight, produced, and slightly elevated posteriorly; shorter than 

 any antero-posterior diameter. The umbones are small, elongate, compressed, 

 pointed, incurved, contiguous, very slightly raised above the rest of the shell, and 

 placed far forwards. From the umbo a well-marked angular erect ridge passes 

 downwards and backwards obliquely to the postero-inferior angle, separating the 

 compressed and hollowed dorsal slope from the rest of the shell. Another erect 

 angular ridge passes directly backwards, parallel to the hinge-line ; and it 

 separates the well-developed, narrow, elongate escutcheon from the dorsal slope. 

 Midway between these two ridges is a third, less marked than the others, which 

 bisects the dorsal slope, and terminates in the angular projection at the centre of 

 the posterior margin. Anterior to the main oblique ridge the shell is gently 

 convex, but is compressed slightly about its centre by a shallow sinus, which ex- 

 tends to and may indent the inferior margin. 



Interior. — The anterior adductor muscle-scar is large and oval, deep, and 

 rounded behind by a curved ridge ; the posterior scar is very shallow, placed close 

 to the hinge-line, but remote from the posterior end. The hinge-plate is unknown 

 in front, but has a long rolled edge behind. The pallial line is entire. Interior of 

 valve smooth. Shell thin. 



Exterior. — The surface of the valves is adorned with concentric lines and 

 lamelljB of growth, close, fine, numerous above in young shells, but becoming 

 gradually coarser and subimbricate as they approach the lower margin. All the 

 lines of growth become much less marked as they pass over the oblique ridge, 

 where they are bent suddenly upwards on themselves, and pass to the superior 

 border, becoming bent somewhat forwards at a very obtuse angle as they cross the 

 oblique line which bisects the dorsal slope. 



Bimensions. — PI. XLIII, fig. 11, from the Carboniferous Limestone of Hill 

 Stebden, Yorkshire, measures — 



Antero-posteriorly . . . • . 41 mm. 



Dorso-veutrally . . . .19 mm. 



From side to side . . . .13 mm. 



Localities. — England : the Carboniferous Limestone of Settle and Hill 



