1844,] 451 



detached substances in the Bidford lias were portions of the 

 animals of the Ammonites which occui' in the same stratum. 



This conjecture has been recently verified by finding a very 

 interesting specimen. It is a species of Ammonite, allied to 

 A. Turneri, Sow., but, as yet, I believe, unnamed, Avhich occurs 

 in a bed of clay, at Defford, Worcestershire, near the middle 

 region of the lower lias. By a fortunate fracture, this spe- 

 cimen exhibits, imbedded in the stone which fills the outer 

 chamber, a substance evidently identical in its nature with those 

 just described. It lies with the convex surface outwards, and the 

 straight side turned towards the mouth of the shell. The portion 

 exposed to view is the cast of the interior surface, which is some- 

 what irregularly waved, but exhibits distinct concentric lines of 

 growth. The whole of this inner surface is black like the Bidford 

 specimens, but portions of the substance itself, which still adhere 

 to the cast, are white and calcareous, showing that in tliis species, 

 at least, the body was of a shelly nature. The slight portions 

 which remain of the outer surface of this thin calcareous plate 

 exhibit fine lines, radiating rather irregularly from the centre of 

 the straight side, in which there is a very small but deep emar- 

 gination or notch. (See the figure b.) 



Judging from the specimens thus repeatedly obtained within 

 the outer chamber of several species of Ammonite, there can be 

 no reasonable doubt that these bodies were appendages of the 

 cephalopodous mollusc which inhabited those shells. I leave it 

 to more expert comparative anatomists to pronounce as to the pre- 

 cise nature of these corneo-calcareous appendages, which were 

 possibly the representatives of the horny girdle described by Pro- 

 fessor Owen as occurring in the recent nautilus, and which aids 

 in the attachment of the animal to the shell. They may also 

 possibly be the equivalents of that " ligamento-muscular disc," 

 which protects the head of the recent nautilus. 



These singular bodies may perhaps throw light on the nature 

 of that much-disputed fossil the Trigonellites or Aptychus. I am 

 aware that Professor Forbes has recently seen some reason for re- 

 ferring the latter fossil to the existing Holothuriadge. But as this 

 supposed affinity is as yet far from being demonstrated, I may be 

 allowed to remark that the two valves of Trigonellites, when ex- 

 panded, closely resemble in appearance the univalve disc which 

 I have been describing ; and when we recollect that Trigonellites 

 have hitherto only been found in formations which also contain 

 Ammonites, and that they have in several instances been found in 

 the interior of Ammonites precisely as in the case of the bodies 

 before us, there is, I think, a fair presumption that these singular 

 bodies are allied in origin and in function to the remarkable fossils 

 here described. 



On referring to a paper communicated by M. Voltz to the 

 Natural History Society of Strasburg, which will be found in the 

 3Iem. de Vlnstitut for 1837, p. 48, it appears that he was ac- 

 quainted with fosisils similar to those before us, and that he also 



VOL. IV. PAKT II. L L 



