PARALLELODON SQUAMIFER. 131 



Modiola. squamifeba, Bigsby, 1878. Ibid., p. 307. 



— (Ctpeicaedia?) squamifeka, Etheridge, 1885. British Fossils, part 1, 



Palaeoz., p. 285. 



Specific Characters. — Shell subarciform, tumid, transversely oblong, wider in 

 the dorso- ventral direction behind than in front. The anterior end is very short, 

 and is the narrowest part of the shell. The shell is moderately convex, but above 

 is hollowed out just in front and below the umbonal swelling. The junction with 

 the hinge-line is rounded ; the anterior border is subelliptically curved, the lower 

 limb descending rapidly downwards and backwards, and joining imperceptibly the 

 lower margin, which is almost straight, and is directed backwards and slightly 

 downwards. The posterior border is obliquely truncate from above downwards 

 and backward, straight above, but very bluntly rounded below, so that there are 

 two subangular points, one above, a little below the centre, where the straight 

 portion of the posterior border joins the curved, and one below, where the 

 posterior and inferior borders join. 



The hinge-line is straight, equal in length to about four-fifths of the greatest 

 length of the valve ; elevated behind, and joins the posterior border at an obtuse 

 angle. 



The umbones are very blunt, incurved, and tumid, not contiguous, raised above 

 the hinge-line, and situated in the anterior fifth of the shell. They are not mar- 

 ginal, but a narrow, elongate area exists between them and the edge of the valves. 



The valves are evenly swollen ; but there is an almost obsolete compression a 

 little in front of the middle line, marked by a very slight irregularity in the 

 surface-markings. A well-defined posterior umbonal ridge, starting from the 

 apex of the umbo, passes backwards and downwards to terminate at the junction 

 of the straight and curved portions of the posterior border. Above this line, and 

 between it and the elevated posterior portion of the hinge-line, the valve is 

 compressed and hollowed so as to be concave. The tumidity of the shell extends 

 close up to the posterior border, and the valves are close all round. There 

 appears to have been a byssal notch in front. 



Interior. — No specimen shows the position and character of the muscle-scars. 

 The hinge-plate is thickened. The extreme anterior portion is not known. 

 Just beneath the umbo there is a transversely elongated portion, which behind 

 divides into four or five elongate, slightly diverging ridges, separated by grooves, 

 which form the posterior lateral teeth. 



Exterior. — The surface is adorned with few (ten to twelve) subequidistaut, 

 narrow, regularly elevated, imbricating ridges, separated by broad, flat, almost 

 smooth spaces. These ridges are oblique to the long axis of the shell, and, though 

 moderately close in front, separate as they pass over the shell from before back- 

 wards, and are continued over the posterior umbonal ridge to terminate in the 



