5rb YORKSHIRE TYPE AMMONITES Ecb. 



51. AMMONITES ATHLETICUS, Simi-son 

 (Plates LIa,b) 



Original Dcscriplivn 

 " i8y. A|mmonites] athleticus. |M. Simpson, 1855, 102.] 



" This resembles A. communis, hut more robust ; the ribs are sharper, 

 and i7iore elevated, some s])lit in two on the outer margin of the whorl, 

 others pass over the back undivided ; inner margin ol the whorls promi- 

 nent ; aperlme ovate ; diameter 4 inches. 



A dditional Details 



Simpson, 1884, 82, adds to first part of sentence " is " after " but " ; 

 adds " M. L. Hawsker " at end of description. He places the species 

 with those which " have a family resemblance to A. communis : — whorls 

 narrow, exposed, with numerous slender, annular ribs, which generally 

 split in two on the back " (j). 81I. 



Remarks 



Stages, conch, serpenticone : periphery, i ; ornament 4. .According 

 to the metatyi)e (PL LIb, f. i) the young shell is a fine ribbed form, and 

 there is anagensis (? renewed) of the costa;. 



The genus is Dacfylioceras, Hyatt, 1867, 95 ; family Dactyloidie, 

 Hyatt. 



The geological position is presumably the very toj) of the Middle 

 Lias, Simpson's Div. a. 



Result 



D.\CTYLiocER.\s ATHLETicuM, SiMPSON sp. 1855, Domerian, [aciiliim 

 zone ?] Hawsker, near Whitby. 



