256 SCALPELLUM RUTILUM, 



Rostrum, unknown ; but one probably existed. 



Upper Latera, of large size, elongated, quadrilateral, 

 approaching to diamond-shaped, with the angles rounded, 

 nearly twice as long as broad; almost flat; upper half 

 acuminated, lying between the scuta and terga; the 

 lower half broad, forming a rectangular projection lying 

 between two latera of the lower whorl. The umbo is 

 near the apex, the greater part of the growth being down- 

 wards, but the valve is added to a little, round the two 

 sides of the apex ; these additions do not take place in the 

 early stages of growth, (as explained under S. vulgare,) 

 and, therefore, they form a depressed rim. 



Rostral Latera, almost exactly triangular, curved; 

 basal margin furnished with a just perceptible rim. 



Infra-median Latera, quadrilateral, sides unequal in 

 length ; the carino-basal margin being the longest ; in 

 area not quite twice double the rostral latera; directed 

 obliquely upwards. 



Carinal Latera, sub -triangular, produced upwards, 

 with the apex rounded, and the two lateral margins hol- 

 lowed out ; the basal margin exceeds a little in length 

 the basal margin of the rostral latera. The umbones of 

 these two latera are seated at their basal outer angles, so 

 that the growth of the valves is towards each other and 

 upwards. The umbo of the infra-median latus is seated 

 at the baso-rostral angle, and hence the growth is obliquely 

 upwards. The umbones of the rostral latera must have 

 been close together, over the unknown rostrum. 



Length of capitulum about ^th of an inch. 



Peduncle, only small fragments are preserved; the 

 calcified scales are small, closely imbricated, several of them 

 together only equalling in length the basal margin of 

 the rostral latera. Each scale is thin, transversely elon- 

 gated ; basal imbedded portion straight ; upper margin 

 rounded. 



Mouth. — Labrum with the upper part highly bullate, 

 forming an overhanging projection ; palpi apparently small 

 and narrow. 



