VARIETIES OF OYSTERS. 189 



another specimen that is barely 2 lth of an inch long. The 

 young are attached by a byssus. They are quite smooth, 

 and in the place of ribs a few fine white lines radiate from 

 the beaks, as is not infrequently seen in P. similis. 



This might be considered, by the advocates of a theory 

 which was once put forward in the " Vestiges of Creation," 

 a case of arrested development as regards P. similis ; but 

 they ought to be aware of the fact that both these species 

 of every age inhabit the same spots and yet retain their 

 own distinctive characters. One species never grows or 

 merges into the other. The young of P. maximus may be 

 known from P. similis of the same size by the upper valve 

 in the former being flat, and in the other convex, as well 

 as by the inequality of the ears in the first-named species. 

 -It bears a considerable resemblance to a young Am'cula, and 

 shows the affinity which exists between that genus and the 

 Pectinidae. The adults seem not to have the power of 

 spinning a byssus, nor to have any occasion for it. Their 

 solid shells can withstand a good deal of buffeting by the 

 tide ; if they were slighter, they would require the cable of 

 a Pinna to hold them on their anchorage-ground. The 

 substance of the shells is very durable. I have had some 

 of the deep valves in frequent use during the last eighteen 

 years, for scalloping oysters ; and although they must have 

 been baked in an oven at least five hundred times, they are 

 as perfect and serviceable as ever. The prettiest specimens 

 come from Dublin, Cork, and the Channel Isles. This 

 species belongs to the genus Vola of Klein. The young is 

 the P. laevis of Pennant and the older British concho- 

 logists. 



P. Jacobaeus (the famous " pilgrim " scallop) was at 

 one time erroneously supposed to be a native of these seas. 



