376 THE LIAS AMMONITES. 



Brachiopoda. Annelida. 



Mliynchonclla variabUifi, Scliloth. Ditrypa quinquesulcata, Miinster, 



Crinoidea. 

 Fentacrinitis scalaris, Goldf. 



Aegoceras poLYiMORPHUM, Quenstedt. PI. XL, figs. 1 — 3. 



Ammonites polymorphus, Quenstedt. Cephalopoden, p. 86, tab. iv, fig. 



13, 1849. 

 — — LiNEATUs, — Uer Jura, p. 128, tab. xv, fig. 14, 



1858. 



Diagnosis. — Shell discoidal, compressed, with numerous — about seven — whorls, which 

 are slightly involute, and have their sides covered with innumerable fine hair-like 

 striations, which arise above the spiral suture and ascend obliquely forwards towards the 

 siphonal area, over which they pass and join the strise from the opposite side. Shell 

 extremely thin, leaving all the markings on the mould ; body-chamber occupies nearly an 

 entire whorl. 



Dimensions. — Transverse diameter 45 millimetres ; width of the umbilicus 22 milli- 

 metres ; height of the aperture 15 millimetres; transverse diameter 9 millimetres. 



Description. — This is a very difficult fossil to determine, as the specimen is badly 

 preserved, and is the only one that has been found. I have, however, put it well together, 

 and enlarged the drawing two diameters ; the shell is in part existing, and is extremely 

 thin. The whorls are only slightly involute, and have their sides ornamented with 

 numberless fine striations, which arise above the spiral suture and are directed obliquely 

 forwards towards the aperture ; they all pass over the siphonal area, forming a series 

 of little ridges there ; the body-chamber occupies nearly an entire whorl, judging from 

 the portion that remains and what is lost. 



The aperture is oblong, arched above, and flattened at the sides ; there does not 

 appear to have been any lateral processes ; the mouth aperture corresponding with the 

 oblique sweep of the hair-like ribs. 



The lobe-line is not complicated, and resembles the style of Aeg. Jamesoni. The 

 siphonal lobe (fig. 3) is narrow, and as long as the principal lateral lobe. The siphonal 

 saddle is wide, and ends in four foliations. The principal lateral lobe is long, and has 

 several lateral and two terminal branches, both of which have trifid processes. The 

 lateral saddle is smaller than the siphonal, and ends in one large internal and two 

 smaller external foliations. The lateral lobe is very small and ends in three points. 



Affinities and Differe7ices. — This Ammonite so closely resembles Am. polymorphus 

 lineatus, Quenstedt, that after much consideration I have determined to treat it as such, 

 although I confess my disinclination to decide species upon such insufficient evidence as 



