426 Frederick Chapman : 



Eelatinnship to I,, aurita. — The Victorian species generally 

 referred to under the name of L. aurita, Brocchi sp., is closely 

 related to that well-known European type of shell ; but it differs 

 in the following particulars from Brocchi's original figure and 

 description.! The shell is heavier when in the ephebic and 

 gerontic stages ; is more ovate, as well as more oblique, rarely 

 being subtrigonal,'^ as in Brocchi's figure of the Pliocene form ; 

 and is peculiarly striate in an apparently double divergent series 

 on each concentric lamina. The original descriptions of Brocchi 

 and G. Sowerby are here given. 



" Area aurita,^' Brocchi. 



Shell ovate, oblique, narrow above ; concentrically ridged, 

 rugae crowded, elevated. Hinge-line ear-shaped, with a distinct 

 triangular pit. Margin entire. 



" Trigouocoelia insolita,' G. Sowerby. 



Shell subovate, thickened, very oblique, smooth ; ligament pit 

 trigonal, laterally elevated ; teeth few, large. 



In neither of these original descriptions is there any mention 

 of radial striae or ribs. With regard to L. aurita, judging'from 

 a fine series of specimens in the National Museum collection, it 

 is clear that there has been either great latitude in the identi- 

 fication of specimens ranging from the Middle Oligocene to 

 Pliocene, or on the other hand, several species have been con- 

 fused under the one name. For instance, specimens of L. aurita 

 (ex. Krantz coll.) from the Middle Oligocene of Flonheim, 

 Rhenish Hesse, are orbicular to ovate-oblique shells. They are 

 moderately deep, with the surface concentrically ridged, the 

 flats of the ridges being radially striate. The inner margin is 

 flat, but crenulate on the inner edge. Again, examples from 

 the White Crag (Lower Pliocene) of Orford, Suffolk, England, 



1 "Area aurita," Brocchi. Coiichioloifia Fosssile Subapemiiiiae, 1814, p. 48.'5, pi. xi.,' 

 fig. 0. 



■2 III some speciineiis of L. inxolita, lietweeii the hrephic and iieanic stayes the shell 

 underjjoes a change in outline from a broad, semicircular to a decidedly oblique form. 

 This imparts a subtrisfotial asjiect to the earlier h.alf of a full-grown shell, but not to such j 

 a degree as in Brocchi's type of L. aurita. 



