ioob YORKSHIRE TYPE AMMONITES— II Mar. 



ioo. ^GOCERAS? FINITIMUM (Bean MS.), Blake 

 (Plates Ca, b.) 



Original Description 



[J. F. Blake, Ceph., in Tate & Blake, 1876 ; pp. 273, 274.] 



" [P. 273] yEgoceras (?) finitimum, Spec, nov. 



" PL VI, fig. 9. 



" Nearly allied to Mg. raricostatum, but having more the appearance 

 of Arietites semicostatus. 



" [P. 274] The front is elevated, and the numerou sstrong ribs run 

 to an angle in the middle, where, however, they become less marked 

 and are subordinate to the pseudo-keel, to which they are joined. The 

 ribs are closer together than in Mg. raricostatum, and the whorls are 

 more inflated. In another specimen there is a tendency to a tubercle 

 at the turn of the ribs. I have only seen two examples of this in the 

 Leckenby Collection under the name finitimus, Bean MS., which I have 

 adopted. 



" Geological position. — Probably zone of A. Bucklandi, Robin Hood's 

 Bay." 



Remarks 



Proportions, 37, 24, 25, 57 ; substeno-, sublepto-gyral ; sub- 

 cxtremilatumbilicate. 



Stages, conch, serpenticone ; periphery, 3 ; ornament, 4. 



The rounded venter carries slightly v-shaped ribs, whose apices arc 

 connected by a low carina. The ribs on the sides of the early whorls 

 are somewhat strong and somewhat distant for a young stage : they 

 resemble the beadlike ribbing of the young stage of Gagaticeras gagateum 

 (Y.T.A. 78) ; and so the inner whorls have an appearance quite distinct 

 from those of Echioceras, with their many small, very approximate ribs. 



In the last whorl the ribs approximate and lose strength. 



The suture-line is of a simple pattern, with broad and shallow lobes 

 and saddles. 



Genus, Par echioceras, (II, ix) ; family, Echioceratidae, (II, v). 

 Geological position, presumably L.L. 13 : the position suggested by 

 Blake is too low. 



Result 



Parechioceras finitimum, Bean-Blake sp. 1876, Sinemurian, 

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





