n 4 b YORKSHIRE TYPE AMMONITES— II July 



114. AMMONITES BIFRONS, Bruguiere 

 (Plates CXIV a, b) 



First Mention 



[Lister, Martin, Hist. Animal. Angl., 1678, Tract III, [Div. 2], 



Titulus 11, p. 205, tab. 6, f. 2.] 



"Ammonis Cornu, spina in ambitu eminente, striis lateralibus paulo 

 ultra mediant tantum partem Orbis extimi pertingentibus. Hie lapis quatuor 

 digitos in cliametro implet ; at paululum uno digitato crassior est. 



" In extimo ambitu velut spinam, hoc est, unam striam acutam 

 eminentemq;, inter duos profundiores sulcos mediam habet : hujus autem 

 spinae unitas nusquam interrumpitur. 



" Striae vero lateralis curvae procedunt ; at orbis non multo amplius 

 quam tres partes occupant ; in quo magnum hujus speciei discrimen. 



" Neq ; in hoc lapide amplius quatuor orbes numerare potui. Huic 

 lapidi color fere lividus, certe si ex rupibus aluminosis exemti sint : alios 

 autem ex his & sulcos & ferrugineos vidimus. 



" Maxime in fractis articulos quosdam observare licet ; at in nonnullis 

 iidem ipsi etiam extrinsecus apparent sc. quodam opere foliaceo singulos 

 articulos distinguente. Intus fere materia quadam crystalling sulfar- 

 cinantur. Caeterum pars Crustacea interdum ex ferri gleba constat. 



" Horum a. lapidum magnam copiam vidi in rupe aluminosa juxta 

 Whitby agri Eboracensis." [V.E.R.] 



Origina I De scrip tio n 

 [Bruguiere, Encyclop. Method. Vers I, 1789, p. 40.] 



"15. Ammonite a double face. 



" Ammonites bijrons. 



" Ammonites anfractibus compressis externe costatis, interne Icevibus 

 dorso bisulcato, carina obtusa inter media ; Nob. 



Ammonis cornu, spina in ambitu eminente, striis lateralibus, paulo 

 ultra mediam tantum partem orbis extimi pertingentibus ; List, conch, 

 angl, pag. 205, tab. 6, num. 2, fig. bona." [V.E.R.] 



Remarks 



The specimen depicted PI. CXIV a, fig. 2 is most remarkable for its 

 agreement with Lister's illustration and description. It agrees in ribbing, 

 extent of umbilicus, amount of exposure between furrow and contact-line, 

 extent of matrix in centre and almost exactly in fracture of aperture — 

 even to projecting point and break down middle of rib. Suture-lines are 

 indicated in Lister's fig. where this specimen has body-chamber ; but, 

 on other side, is a suture-line which may have been transposed a little 

 too far on (ES broad, L x wide-stemmed, denticulate, incipiently trilobulate, 

 S 1 narrow, L 2 small). 



With description — Lister's measures 2.9 in. (74 mm.), a digitus = 

 0.725 in. ; present specimen is 76 mm. Lister's, " a little thicker than 

 a finger " ; this, 0.8 in. Lister's proportions, T. & F. 74(61), 32, [27], 45 ; 

 this, S. 76, 32, 27, 45. Lister's remarks about partitions, broken parts 

 and crystalline matter (a) are all borne out by other side of specimen, 

 where, too, is what looks like " pars Crustacea " (b). 



