VOL. L.] PHILOSOPHICAL TRANSACTIONS, 26l 



XCIII. Description of a Rare Species of OrthoceratiteSy in a Letter from Dr. 

 Nicholas de Himsel, to JVilliam Watson, M. D., F. R. S. From the 

 Latin, p. 692. 



A species of orthoceratites found in Kelwick near Fulham. The fragments 

 were imbedded in a grey calcareous stone, and the specimens were of various 

 sizes. 



Fig. A, pi, 8. A portion of an orthoceratites, the lower part of which adheres to the stone j it 

 consists of calcareous stone, and gradually decreases to the top. Although from the fragments we 

 might suppose the orthoceratites to be a cylinder, yet the fragments when joined, shew it to be a 

 cone, and it seems tome, from the thickness of its syphon, that this orthoceratites must have been 

 more than two feet long. I have seen a specimen in another calcareous stone found at the same 

 place, of two feet and a half length, but it was so brittle that it was not possible to get it out entire. 

 This portion of orthoceratites is coated by its surrounding shell at a b c. Five joints are visible, 

 which were once the cavities or thalami, and are situated close together, and through them passes 

 on one side a thickish siphon or tube, which in almost all the orthoceratites in my possession is 

 always remote from the centre, but here is situated at the periphery. The siphon lessens gradually, 

 from which circumstance we may judge of tlie length of the cone of this specimen. The inner 

 part of the crust or shell a be which covers the joints, is crystalline, consisting of small irregular 

 sparry crystals. — Fig. b. Another portion in which the joints are thinner, and the siphon placed at 

 the periphery, covered with its shell at a. At b is seen the shelly septum, which proceeding from 

 the superior joint invests the part r s of the siphon. — Fig. b. c. A portion of an orthoceratites of grey 

 calcareous stone, but the siphon consists of sparry fluor finely cryslalized. — Fig. c. Another portion 

 divided through the axis, and with the outer part covered by the shell, marked with slight circular 

 striae. — From the interior part fig. d its internal conformation appears, The smaller siphon xz, 

 placed between the centre and the periphery, appears freed from its surrounding joint half way, the 

 remaining half being covered by the lower joint c d e. The joint a b is filled up by pellucid polygonal 

 crystallized spar ; but the joint c d e is filled by flesh-coloured sparry stone. The superior part of 

 the siphon is shown at x, where the rays going from the circumference to the centre are visible. 

 Between the sparry crystals in the joint a b appear black streaks here and there, which are filled with 

 asphaltum : so likewise the cavity of the joint a b, as well as the convex surface of the joint c e, 

 which is received into the first concavity, are coated by a lamina of asphaltum. — Fig. e. Another 

 part of a larger orthoceratites, shewing its exterior. — Fig. r. Its interior as divided through the 

 middle, with a pretty thick siphon, abc and the other slight streaks are the diaphragms separating 

 the joints ab which constitute the siphon, and surround the thinner membrane of the siphon, which 

 is still apparent at o and p. These diaphragms are thicker in the vestiges of the siphon, and are 

 placed on each other at their lower part. The siphon in this specimen is situated between the 

 centre and periphery. — Fig. g. The striated calcareous matter which filled the siphon, and its in- 

 terior part, looking toward the centre opposite the periphery. — Fig. f . The posterior side, nearer 

 the periphery. — Fig. i. The concave part of a large joint in which the whitish particles of the tes- 

 taceous diaphragm now crystallized m n r are seen, with the siphon passing through them. — Fig, k. 

 Another portion of a large orthoceratites, shewing its external appearance, with the siphon g placed 

 at the periphery. The diaphragms are here seen proceeding on each side from the joints, joining 

 each other, and concealing the siphon from the exterior part, a is a small portion of the thickish 

 shell, with which this orthoceratites is still covered. 



