124 GEOLOGICAL MEMOIRS. 



each other. In reference to the large crystalline lens which cha- 

 racterises the eye in naked Cephalopods, the parts in question can 

 only be compared, from their size, with the exterior laminae of the 

 outer division of the lens, in which case the larger and denser 

 inner division of the lens has not at all been preserved ; which is 

 by no means a probable occurrence, and induces me to reject this 

 analogy. If we compare them to the strong external tunic of the 

 eye, their outward convexity would lead to their being referred to 

 the cornea. But this part, in all existing Cephalopods, is a modi- 

 fication of the integument, and continuous with it, presenting a less 

 degree of convexity than in the fossils, less thickness, and a less 

 definite extent. Viewing, however, the relative position/ form, and 

 structure of the parts under consideration, the most probable con- 

 clusion respecting their nature appears to me to be that which 

 refers them to the anterior or external tunic of the eye-ball, in 

 which case they indicate a thicker, stronger, more distinct, more 

 extensive, and more convex cornea in the Belemnite than in any 

 known existing Cephalopods. 



The evidence afforded by the above described specimens of the 

 paucity in number, and superiority in size and complication, of the 

 cephalic tentacles of the Belemnite, as compared with the Nautilus, 

 yields another proof of the constancy of the laws of organic cor- 

 relation ; the very numerous, small, and comparatively simple ten- 

 tacula of the Nautilus which illustrate the principle of vegetative 

 or irrelative repetition, being associated with an essentially inferior 

 type of Cephalopodal organization, into which an internal shell, a 

 thick muscular mantle, pallial fins, and an ink-secreting apparatus 

 do not enter. 



In comparing the different forms of Cephalopods that have suc- 

 cessively appeared and perished since the deposition of the Lias to 

 the present time, we do not find that the highly complex organisa- 

 tion of the cephalic arms exhibited in the Onychoteuthis has been 

 attained by or through progressive gradations, typified by the 

 organisation of intermediate forms, for the ancient Belemnites 

 manifested the uncinated armature as perfectly as the most formi- 

 dable of the existing Onychoteuthides. Nor were true Calamaries 

 with uncinated arms absent in those primaeval seas which were 

 tenanted by living Belemnites, Ammonites, and other extinct 

 forms of Cephalopoda. The existence of naked Cephalopods of 

 the family Teuihidce in the oolitic secondary formations has been 

 for some years demonstrated by the well-preserved and recog- 

 nisable remains of the ink-bag, the gladius or horny pen, and the 

 horny hooks developed from the acetabula of the cephalic arms. 



In conclusion, if we compare the Belemnite as now restored, 

 not conjecturally, but by observation of phenomena, with the 

 known existing forms of the Dibranchiate or higher order of 

 Cephalopods, in which its right of place can no longer be disputed, 

 we shall first recognise in the outwardly concave plates and margino- 

 ventral siphon of the chambered shell of the Spirula, the analogue 

 of the hydrostatic part of the shell or phragmocone of the Belem- 



