BELEMNITELLA. - 9 



covered with small granulations ; vascular impressions strongly marked in the young shell, 

 but somewhat concealed by the granulations in the full-grown shell. 



The external form of B. qiiadrata is nearly the same as that of some varieties of 

 B. mucronata ; so that worn specimens which have lost both their outer surface and the 

 upper part of the alveolus may easily be confounded ; and there has been confusion in 

 consequence in the synonyms. But it is well distinguished both by the granulations 

 of the surface and the square opening. 



The lower part of the alveolar cavity, lined with a distinct, smooth, shelly layer, is of 

 the form of a rounded cone, about a quarter of an inch deep ; above this, the cavity 

 suddenly widens out, and changes its character; it is irregularly four-sided, and the 

 surface has no special lining, but is roughened by the rings of growth of the shell. 

 The fissure is shallow, and reaches to the top of the lower division of the cavity. 

 Unfortunately, the Phragraacone of this species is not known ; it would probably corre- 

 spond in form with the lower part of the cavity only. 



Length, 2^ inches ; greatest breadth, yV^^^^ of an inch ; cavity, f ths of an inch, of 

 which the broader part occupies J th, and the narrow rounded cone, ^th of an inch. 



B. quadrata is found in the middle beds of the chalk of the counties of Kent, Surrey, 

 and Sussex, but is no where a common species. It has also been found in the upper 

 chalk of Northfleet. 



It occurs, according to M. D'Orbigny, in the white chalk of Rheims in France, and 

 of Vise in Belgium, 



4. Belemnitella plena, Blainv., Sp. Plate I, figs. 12 — 16. 



Breyn. De Belemnitis, fig. 15? 

 Belemnites plenus, Blainville. Belemnites, t. i, fig. 6. 



— LANCEOLATXJS, Sowerby. Min. Conch., t. 600, figs. 8 and 9. 



— — Geinitz. Quadersansteingebirge, t. vi, figs. 3 — 5. 

 Belemnitella vera, D'Orbigny. Paleont. Fran?. Terr. Cret., Suppt., t. ii. 



B. testa elongatd fusiformi, subleevi, superne rotundato-trigond canaliculatd, medio 

 rotundatd dilatatd; apice acuminato. 



Shell elongated; when young cylindrical, with a tapering point; when full-grown 

 fusiform, swelling out below the middle, and tapering below to a point ; front marked 

 with a slight furrow ; a broad longitudinal depression on each side of the back, giving 

 somewhat of a three-sided form to the upper part of the shell. All the specimens have the 

 walls of the alveolar cavity broken off, leaving usually a projecting conical end, in the 

 centre of which the point of the alveolus may be distinguished. 



The specimen, fig. 12, belonging to Mr. Morris, has fortunately the lower part of the 

 cavity preserved, but not enough to show any trace of a fissure ; therefore the supposed 

 fissure figm-cd by M. D'Orbigny, pi. ii, figs. 2, 4, and 7, in a more truncated specimen, 



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