216 



THE SEA SHORE 



rays being very prominent, each bearing a number of calcareous 

 spines arranged in a single row. We give an illustration of this 

 species, together with two sketches to show the nature of the teeth 

 of the shell. 



In addition to the two species named, we have the red-footed, 

 C. rusticum, which can suddenly turn itself over by the action of 

 its powerful pedal organ ; the Banded Cockle (C. fasciatum), a very 



small species distinguished by 

 the brown bands of the shell ; 

 and a still smaller one (C. pyg- 

 mceum), with a triangular shell, 

 occurring on the Dorset and 

 Devon coasts (fig. 146). 



Passing now to the AsipJio- 

 rtida, we deal first with the 

 family A rcadce. These include a 

 number of shells which, though 

 very variable in general form and 

 appearance, may all be recog- 

 nised by the long row of similar 

 comb-like teeth that form the 

 hinge. The shells of this group 

 are regular in form, with equal 

 valves, and are covered with epi- 

 dermis. The mantle of the ani- 

 mal is open, the gills are united 

 by a membrane behind, and the 

 foot is large, curved, and grooved. 

 One of the prettiest shells 

 in the family is Pectunculus 

 glycimeris, which reaches a 



length of about two inches. The shell is grooved in the direc- 

 tion of the lines of growth, and there are also very delicate 

 striations running radially from umbones to margin ; and the 

 ground colour of white or pale yellowish is beautifully mottled 

 with reddish brown. We give a figure of this species, together 

 with a drawing of the peculiar and characteristic teeth, but a 

 more typical shell of this family may be seen in the Noah's Ark 

 (Area tetragona). This shell is almost quadrate in form, swollen, 

 and strongly ribbed. The hinge is straight, with many comb-like 

 teeth increasing in number with the age of the shell ; and the 



FIG. 148. Pectunculus glycimeris, 



WITH PORTION OF VALVE SHOW- 

 ING TEETH, AND Area tetragona 



