CUCULLAA. 53 
Deseription.—Shell rather stout, rounded, nearly equilateral. Anterior 
margin rounded; posterior a little truncated ; ventral curved. Umbones promi- 
nent, incurved. Hinge-area relatively broad. Posterior part of shell sharply bent. 
Ornamentation consists of strong, equal, regular ribs, separated by broader 
grooves; the grooves are crossed at regular intervals by fine concentric ribs. 
Central teeth transverse; lateral parallel to the hinge-line. Margins of valves 
coarsely toothed. 
Measurements : 
Length . : ; : , : : , - 20cm: 
Height . F : ; : ' : ‘ : iStees 
Remarks.—This form, which at present is only known by a few rather 
imperfect specimens, appears to be clearly distinguished by the character of its 
ornamentation. 
Cucullexa errans, Keeping, nom. nud., I think undoubtedly refers to this 
species; the name was used in the earlier part of Keeping’s work (vide supra), 
and the remarks there made concerning it agree perfectly with those given later 
in connection with C. vagans. This view is further supported by the fact that 
on the back of the tablet which bears the type-specimens of C. vagans there is 
written in Keeping’s handwriting ‘‘ C. errans, W. K.”’ 
Types.—In the Woodwardian Museum, Cambridge. 
Distribution —Lower Greensand (black grit nodules) of Upware. ? Spilsby 
Sandstone of Spilsby. 
Sub-genus—DIcraNnovonta, s.-g. nov. 
Shell stout, subquadrate or rounded, Hinge-area broad. Hinge-plate large, 
curved; central teeth transverse; lateral teeth long, 
parallel, often bifurcating. No posterior adductor plate. 
Type.—Cucullea donningtonensis, Keeping (Pl. X, figs. 11—14; Pl. XI, fig. 1). 
Claxby Ironstone. 
curved ventrally, nearly 
The form described by Keyserling,' and by F. Schmidt,’ as Pectunculus petschore 
probably belongs to this sub-genus. The latter author was inclined to regard it 
as the type of a new genus. 
1 «Reise in das Petschora-land’ (1846), p. 306, pl. xvii, figs. 5, 6. 
“ Resultate der Mammuthexpedit.,” ‘ Mém. Acad. Imp. Sci. St. Pétersbourg,’ ser. 7, vol. xviii, 
No. 1 (1872), p. 151, pl. i, fig. 14; pl. iiia, fig. 17. 
no 
