APTYCHI. 483 



John Leckcnby, F.G.S., of Scarborough, to the Royal School of Mines Museum, London, 

 as a very good type of a rare Yorkshire species. 



Locality and Stratiyraphical Position. — Amaltheus lenticularis is found in the zone 

 of Amaltheus spinatus in the rich Ironstone beds at Eston, and Upleathara, near Saltburn, 

 also at Hawsker. I am indebted to my friend Mr. E. T. Newton, F.G.S., Palaeontologist 

 to the Geological Survey, for calling my attention to this specimen now figured for the 

 first time. 



In the preceding portions of the Monograph 1 I have referred to the remarkable 

 curved plates, sometimes calcareous and sometimes horny, occasionally found in position 

 within the shell of the Ammonite, and I have drawn attention to the fact that the 

 distinctive character of the structure of the plates is associated with modifications of 

 the septa and of the general ornamentation of the shell, as well as with geological 

 position. Since these remarks were in type, I have had drawn on Plate LXXXVIII 

 four specimens derived from the Oolitic and Liassic beds, which may be taken as 

 representatives of the calcareous and divided forms {Aptychi) and of the horny and 

 undivided ones {Anaptychi). 



Figure 1 of Plate LXXXVIII represents an almost perfect Aplychus from the upper 

 beds of the Inferior Oolite of Leckhampton Hill. It consists of thin shelly laminae, 

 exhibiting lines of growth, and is in length 140 millimetres and in breadth 95. I 

 imagine it must have belonged to Cosmoceras Parlcinsoni. In my cabinet is an example 

 of this species from the upper beds of the Inferior Oolite at Halfway House, near Yeovil. 

 The specimen is 500 millimetres in diameter, and has its last chamber transversely 

 fractured, the curve and size of which agrees very nearly with that of the Aplychus. 



Figure 2 is a drawing of an Anaptychus, which I dislodged from the outer 

 chamber of a large Arietites stellaris, taken out of the Lower Lias strata of Charmouth. 

 This body is bell-shaped, corneous, highly undulated on the surface and displays the 

 lines of growth. It is difficult to understand how bodies so irregular, as are many of 

 the Anaptychi, could have fitted the internal surface of the final chamber. 



Figure 3, from the British Museum, but without locality, is another of the bell- 

 shaped Anaptychi. It has a thickened central column and lateral biflexed undulations 

 passing off on each side. The upper part of the body runs out into a pear-shaped 

 process. 



Figure 4 is also from the British Museum, but has no label of locality. The fossil 

 appears to have been in its original condition a symmetrical structure, and resembled in 



1 Pp. 182 — 185, general statement; p. 269, account of forms belonging to Arietites; p. 307, 

 to Aegoceras ; p. 383, to Amaltheus ; p. 430, to Harpoceras ; p. 472, to Stephanoceras. 



