G. C. Crick — Note on Ammonites enomphalus, Sharpe. 251 



of Hall, besides withdrawing tlie mollusc from the genus PaJ<B- 

 anodonta, to wbicli Amalitsky attached it in 1895. 



The following dimensions of the known examples of Archanodon 

 JuTcesi and A. Catshillensis (largest specimens selected) may be of 

 interest for comparison : — 



Archanodon JuTcesi. — Ireland : length, 185 mm. ; height, 75 mm. ; 

 diameter (allowing for closed valves), 24 mm. Northumberland: 

 length, 228mm. ; height, 102 mm. Monmouthshire : length, 140mm.; 

 height, 54 mm. ; diameter (allowing for closed valves), 34 mm. 



Archanodon Catshillensis. — Length, 155 mm. ; height, 67 mm. 



Horizon. — The Monmouthshire specimens are in a matrix of 

 reddish-brown sandstone grit of a somewhat coarse character, 

 highly micaceous, and with a tendency to pulverize when handled. 

 This formation was probably of contemporaneous deposition with 

 the ' Yellow Sandstone ' Series of the South of Ireland, and may 

 consequently be regarded as of Upper Old Eed Sandstone age, and 

 not of a lower horizon as originally surmised when the present 

 specimen was exhibited at the Geological Society. 



III. — Note on Ammonites euomphalus, Sharpe. 

 By G. C. Crick, F.G.S., of the British Museum (Natural History). 



THE name Ammonites euomphalus was given by Sharpe ^ to an 

 imperfect though unique specimen from the Lower Chalk, Man 

 of War Cove, on the coast of Dorset. This example (according to 

 Sharpe) originally belonged to E. H. Bunbury, Esq., but now forms 

 part of the British Museum Collection [No. 50,158]. 



It is fairly well represented in the figures accompanying Sharpe's 

 description, which is as follows : — " Shell gibbous, with a broad 

 flattened back and angular whorls, crossed by numerous unequal 

 tuberculated ribs, which bifurcate at the back ; the ribs are about 

 twenty in number on the side of the whorl, alternately larger and 

 smaller ; the larger ribs bearing a small tubercle near the umbilicus, 

 and a strong spine at the edge of the back ; the number of ribs on 

 the back is about double that on the sides of the whorl, two 

 springing from each spine, curving forwards and meeting again at 

 the opposite spine ; about every fourth dorsal rib is larger than the 

 others, and bears two slight tubercles : umbilicus broad and funnel- 

 shaped, leaving three-fourths of the inner whorls visible : aperture 

 transverse and angular : septa with four very simple trifid, lateral 

 lobes, and the lateral saddle very small." 



As mentioned by Sharpe, the shell is " crossed by numerous 

 unequal tuberculated ribs .... alternately larger and 

 smaller .... the larger ribs bearing a small tubercle near 

 the umbilicus, and a strong spine at the edge of the back," but the 

 smaller ribs also have tubercles similarly situated, though relatively 

 very much smaller than those on the larger ribs. The pairs of ribs 

 which pass across the periphery and connect the strong spines ou 



1 D. Sharpe: " Foss. Moll. Chalk of England" (Mon. Pal. Soc), pt. ii (1854), 

 p. 31, pi. xiii, figs. 4a-e. 



