SCALPELLUM. 33 
quadratum. Still closer is the affinity with the cretaceous S. fossula ; the carinee of both 
have intra-parietes; the tectum is distinct from the parietes, which latter are either 
channelled or concave; the trapeziform scuta of S. quadratum, fossula, and maximum, are 
unmistakeably alike, and even more striking is the resemblance of the carinal latera ; 
there can be no doubt of these three species belonging to the same genus, and having 
the same number of valves, namely, as I have shown under 8. guadratum and. fossula, 
probably twelve, 
Geological History. This species, with its varieties cylindraceum and sulcatum, is very 
common in the Upper Chalk strata of Norwich; I have seen one specimen from the Upper 
Chalk of Northfleet, in Kent. It is common in the sandstone beds of Scania, which I am 
assured by Professor Forchhammer, are without doubt equivalent with the Faxoe beds, and 
therefore belonging to a stage above our flinty chalk. I have seen, also, one specimen, 
belonging, I believe, to this species, from the same stage in Westphalia; and another from 
Belgium ; it is also common at Gehrden, in Hanover, in the ‘Oberer Kreidemergel’ of 
Roemer. : 
SCALPELLUM MAXIMUM, VAR. CYLINDRACEUM. ‘Tab. II, fig. 2. 
S. parte superiore carine liberé prominente, parte interiore intra-parietibus rotundatis, 
inflexis, ita repleta, ut pene cylindrica fiat; superficie externa lavi, tecto parietibusque pane 
confluentibus. 
Carina, with the upper portion projecting freely, and with the inside filled up by the 
rounded inflected intra-parietes, so as to be almost cylindrical; exterior surface smooth, 
with the tectum and parietes almost confluent. 
Amongst the specimens from Norwich, ‘a differed from the others in being a little 
more elongated and smoother, in the parietes becoming almost confluent, low down on the 
valve, with the tectum, and in the intra-parietes being very little developed. On the 
internal face this variety presents its most remarkable character; for a large upper portion 
of the valve must have projected freely, and the intra-parietes, instead of forming a 
thin wall on each side, are thickened, rounded, and turned inwards, so as almost to meet, 
and thus to fill up the original concavity of the valve. Hence a section (fig. 2, c) of 
the upper part, some way below the apex, is almost cylindrical, or more strictly oval 
with the longer axis in the longitudinal plane of the animal, with either a wedge-formed 
hollow, or a mere, almost closed, cleft on the under side, penetrating not quite to the 
centre of the solid valve. The two specimens differ, one in being in a transverse line 
exteriorly much depressed, the other highly arched or convex, and internally still more 
conspicuously in the degree to which the intra-parietes have filled up the upper part. In 
one of the specimens there is even a difference on the opposite sides of the same individual 
valve. Notwithstanding these varieties, I should have much hesitated to have ranked 
e 
