SCALPELLUM. 33 



quadraium. Still closer is the affinity with the cretaceous S. fossula ; the carina3 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 S. quadraium 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 om- flinty challc. 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 carina libere prominente, parte interiore intra-parietibus rotundatis, 

 inflexis, itd repletd, ut pane 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 suiface smooth, 

 with the tectum and parietes almost confluent. 



Amongst the specimens from Norwich, two 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 tne 

 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 difler, one in being in a transverse fine 

 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 



