342 report — 1879. 



cation might be found in the views propounded by the many learned geologists who 

 had preceded him. 



The variety of forms which the aptychi assume appears to indicate almost a 

 generic modification in the forms of the animals occupying the shells to which they 

 belong. In the earliest known British ammonite (the A . planorhis) it is in one lobe 

 only, with coarse concentric lines of growth, finer longitudinal strife being visible 

 by aid of the lens. In this species an inner layer is always black, as if stained by 

 the pigment of cuttle fish, a circumstance seen also with some others from the upper 

 has. The author considered this might be due to the presence of animal matter to 

 which the lobes were originally united. Although so many ammonites were known 

 in the lower lias, he was only acquainted with the above species from this formation. 

 In the upper lias they were oftenest found in connection with ammonites in a bed 

 of about a foot in thickness, which he had called the Saurian and Fish bed, and in 

 the clays which surround it. From this bed he had obtained microscopic ammo- 

 nites, in which the aptychus might be seen far back in the outer chamber. They 

 were found also in another remarkable way. Larger ammonites were deposited in 

 the upper portion of this bed, but the shell itself has disappeared, leaving usually 

 only the mould where it lay. It has not been washed out, but dissolved away, 

 probably by carbonic acid. Strangely enough, in many examples the aptychus 

 which was in the interior of the shell has not been affected by this action, and the 

 siphuncular tube also has been left passing round its whorls where once were its 

 many chambers. The fact that the aptychus belongs to the ammonite is shown by 

 its presence in such minute specimens, by there never being more than one example, 

 and by a special form being united to each species of ammonite. A remarkable 

 point respecting the siphuncular tube is that it is not the mere tube as usually seen in 

 other ammonites and nautili, but has an envelope of concentric layers surrounding it, 

 increasing considerably its usual bulk. On examining the moulds of Ammonites ser- 

 pentinus the author stated that he was surprised to find that their surfaces were covered 

 by hundreds of thousands of minute scattered eggs, some apparently hatched, whilst 

 other larger ovate bodies were possibly an advanced or metamorphosed form of the 

 same animal. Amidst these scattered eggs there were also strings of similar eggs, 

 though at times somewhat compressed and varying in size, lines of them lying to- 

 gether. In one instance the siphuncular tube passes over the aptychus, but they 

 had not been noticed actually in connection. The question arose to the author, 

 ' What have the aptychi and the tube to do with these eggs ? Can either or both 

 be an ovarian sac ? ' 



Minute examinations of different forms of aptychi were then made, when it was 

 found that in every instance they were almost entirely cellular, and the author was 

 able to extract from them lines of cell-tubes, differing in scarcely any respect from 

 the egg packets lying amidst the scattered eggs on the Ammonites serpentinus of the 

 upper lias. Aptychus lsevis of the Kimmeridge clay had yielded him great numbers 

 of globular bodies which, though converted into iron pyrites, were undistinguishable 

 from the eggs of the upper lias. In smaller numbers they were also found in 

 Aptychus lamellosus. Both tubes and clusters of eggs were also obtained from the 

 curiously formed Aptychus Didmji, whose curved and bold lines of growth gave a 

 twisted form to the tubes. Microscopic sections of Aptychus Didayi and A. Icevis 

 showed what appeared to be eggs within their cellular tubes. The thinness of the 

 structure of the upper lias species might seem almost to preclude this tubular cha- 

 racter, but on examining unworn specimens it may be seen that the laminse fold 

 over like Venetian blinds, and that their edges are fringed with tubes, coming to the 

 surface, and which pass down obliquely through them. When the corneous layer 

 which covers the concave side of the aptychus lobes is removed, myriads of minute 

 cells are visible ; these, as they pass through the body to the convex surface, 

 bifurcate and enlarge. 



The layer referred to is as thin as tissue paper ; the author had been able to 

 remove and preserve an example of this layer which, under the microscope, was a 

 beautiful object; comparing small tilings with great it looked like the gnarled sur- 

 face of a walnut-wood table, and showed the structure with openings in the centre 

 .of concentric circles passing round the tubes immediately below. 



