SCALPELLUM. 87 



6. ScALPELLUM HASTATCM. Tab. II, fig. 13. 



S. carina intra-parietibus, intra paulvlum positis, instructd ; valvd totd inirorsum valde 

 arcuatd, marline interno non recto ; margine hasali acuto, lanceolato ; valvd tenui, lavi, 

 tecto transverse leniter arcuato ; parietibus a tecto vix disjunctis. 



Carina having intra-parietes set a little inwards ; whole valve much bowed inwards, 



with the inner margin not straight; basal margin sharply pointed, spear-shaped; valve 



thin, smooth ; tectum in a transverse line flatly arched ; parietes barely separated from 



tectum. 



Grey Chalk, Dover, Mus. Brit. 



Carina smooth, narrow, furnished with intra-parietes, widening gradually from the apex 

 downwards ; extremely much arcuated, so that the uppermost part, of which none, or very 

 little, projected freely, is at right angles to the basal part. Not only is the dorsal surface 

 considerably arcuated, but so are the iimer margins, which is much more important. Basal 

 margin sharply pointed, with the two edges meeting each other at about an angle of 75°. 

 Roof with the two sides continuously and flatly arched ; parietes rather narrow, slightly 

 concave, barely separated from the tecta : the concavity of the parietes, as seen on the basal 

 margin, together with the sharpness of the central portion, makes the lower part of the 

 valve spear-shaped. The intra-parietes are set a little within the parietes ; they extend 

 down to about two thirds of the entire length of the carina, and not to the basal margin of 

 the parietes : they are widest at about only one fourth of the entire length of the carina 

 from the apex, and here they equal in width the rest of the valve. Internally the valve 

 is, in the upper part, owing to the wide intra-parietes, deeply concave ; in the lower part, 

 only slightly so. 



Length of carina, measured along the chord of the arch, -75 of an inch. 



Affinities. This species certainly comes very near to 8. maximwn ; but I think it is 

 distinct, and is its representative in the Grey Chalk. I have seen only a single specimen. 

 The carina differs from the former varieties and species in its smoothness, thinness, in 

 the acumination of the basal margin, in its much arcuated form, and more especially (for 

 this, probably, would greatly influence the outline of the terga,) in the inner margins being 

 also thus arcuated. 



7. ScALPELLUM ANGUSTUM. Tab. I, fig. 2. 



XiPHiDiUM ANGUSTUM. Dixon. Gcology of Suffolk, tab. xxviii, fig. 9. 



S. carind angustd, introrsiim valde arcuatd; tecto a parietibus rectangule inflexis costd, 

 (ut videtur) disjuncto ; intra-parietibus usque ad dimidium valvce pertinentibus, deinde 

 oblique et abrupte truncatis ; margine basali acute cuspidato. 



