95b YORKSHIRE TYPE AMMONITES— II Jan. 



95. AMMONITES SOCIALIS, Simpson 

 (Plate XCV) 



Original Description 

 " 16. Afmmonites] socialis. [M. Simpson, 1855, p. 39]. 



["I. Without a dorsal keel or furrow. 

 "a. No spines." p. 35.] 



" Volutions several, exposed, outer whorl two-fifths the diameter ; 

 radii irregular, diverging, pass unaltered over the back ; striae fine, 

 longitudinal ; aperture rather ovate ; diameter 4 inches. L.L.— R.H. Bay. 

 Syn. A. plicatilis, Simp." 



Additional Details 



Simpson, 1884, p. 67, adds after name " T. & B. [Tate & Blake], 

 pi. vii., f. 6 " ; has after " L.L." " t [t] " ; omits last sentence. 



Remarks 



Proportions, 112, 33, 29, 40 ; subplaty-, subpachygyral, latum- 

 bilicate. 



Stages, conch, serpenticone ; periphery, 1 ; ornament, 3c and 4c. 



The specimen shows in side view only part of a whorl, which is 

 somewhat obovate in section and carries obscure irregular sized and 

 spaced costae, with intermediate subcostae. The specimen, in fact, 

 shows the stage of costation which in this and like forms intervenes 

 between two tuberculate stages. Blake (1876, vi, 6) depicts such 

 a first tuberculate stage ; Simpson's type shows the subsequent cata- 

 genesis — a costate stage ; and there should follow renewed anagenesis — 

 another tuberculate stage. 



Canavari (1882, 156) suggested possible relationship with Lytoceras 

 bijorme, Sow. ; but the highly complicated suture-line, though only 

 exposed in places and difficult to follow negatives this : it is of the 

 Deroceras pattern. 



Genus, Deroceras, Hyatt ; family Deroceratidae. 



Geological position as given by Simpson appears too high : Blake 

 (1876, 276) says " subzone of A. armatus." 



Result 



Deroceras sociale, Simpson sp. 1855, Charmouthian, [armatum 

 zone], Robin Hood's Bay, near Whitby. 



