40 EOCENE MOLLUSCA. 



tudinally, sometimes the reverse ; the ears are slightly unequal, the pedal one being a 

 trifle the larger. The shell diverges from the umbo at an angle of about 120°, and 

 the divergence of the lines upon the fainter portion of the shell at about 80°. 



The typical specimens of this species are from Selsey, Bracklesham, and Stnbbington, 

 where they attain to full proportions. There are also specimens found in the London 

 clay at Hampstead, assigned to this species ; these are seldom more than half the diameter 

 of the Sussex shell, and may be considered as a variety, which I will call corneolus, PI. IX, 

 fig. 7, d. The difference in magnitude would not of itself be sufficient to entitle these shells 

 to the position of a variety j 1 but there is a slight variation in the right auricle, which is 

 rather more rounded, and in some of the specimens the proportions are different, giving 

 them a more ovate form. 2 



4. Pecten contubernalis, S. Wood. Tab. IX, fig. 8. 



Spec. Char. P. testa tenui, subcorned, orbiculato-depressd, ceqxilaterali, tenuissime striata, 

 sfriis radiatis argutis ; umbonibus acutis ; auricidis subaqualibus, mperne rectangulis, 

 costellatis. 



Shell thin, subcomeous, orbicularly depressed, equilateral, and very finely striated, 

 stria? thin and radiating, beaks acute; auricles nearly equal, and prominently radiated or 

 costated. 



Diameter, l|th inch. 



Locality. Heme Bay {Edwards). 



This shell appears to present differences sufficient to entitle it to an isolated position : 

 the elevated radiations or costa? upon the auricles will distinguish it ; and the whole surface 

 is more strongly marked by the fine, divaricating, and curving stria? with which it is 

 covered, and these extend over the auricles. I have seen but one specimen, which is in 

 Mr. Edwards' cabinet, but this differs so materially that I think it cannot belong to the 

 preceding species. The auricles are comparatively much larger than those of corneus : 

 in that shell their length does not exceed -^ths of the diameter of the valves, while in 

 this species they are ^ths ; and although the young shells of Pecten have generally larger 

 ears, comparatively, than when full grown, a great difference may be seen in specimens of 

 the two species of corresponding size. 



1 Since writing the above, I have seen a specimen of this variety in Mr. Wetherell's cabinet, which 

 measures If inch in diameter. 



2 At p. 72, t. 11, * Anim. s. Vert, du Bassin de Par.,' M. Deshayes has pointed out the confusion that 

 exists among species with the above name, and enumerates not less than seven, but which he considers to be 

 quite distinct. One of these seven (P. corneus, Melville, pi. Ill, figs. II, 12,) very strongly resembles the 

 young state of our shell, corresponding with the Highgate variety (corneolus). 



