j6 IDENTIFICATION. 



radial and faint. It must be aureus or virginetts, and being rayed 

 and spotted with reddish brown, instead of being streaked and 

 blotched with brown and purple, it is evidently the latter. Tapes 

 virgineus it is. Some reader may ask what is its other name ? The 

 answer is that we do not know that it has another. 



Combining our information, we find that the shell is equivalve, 

 inequilateral, yellowish in colour, rayed arid spotted with reddish 

 brown, concentrically striated, the hinge having three cardinal teeth 

 in each valve, the pallial line having a deep rounded sinus, and the 

 muscular scars being oval. It would not take long to arrive at the 

 genus by way of our key, for the indented pallial line takes us at 

 once to the C division, the equivalve shell gives us another long step, 

 the not gaping at either end another, and the ligament wholly 

 external with the three teeth in both valves land us in either Tapes or 

 Venus, which are separable by the shape of the indentations in the 

 pallial line. 



Let us take another shell by the key. It is equivalve, but its 

 valves are of a curious shape and prickly, and have a sort of plate 

 on the back, with two arms stretching out into the interior from 

 where the valves join. The shell, in fact, has dorsal pieces and 

 apophyses, and the apophyses are long. As it is prickly all over, 

 the genus is at once apparent as PJiolas. Taking it the other way 

 round we find the Pholadidae to have a shell gaping at both ends 

 without hinge or ligament, with one or more accessory dorsal pieces 

 an internal apophysis from each beak cavity and the dorsal margin 

 reflected over the beaks. There are three British genera in the family 

 Xylophaga, with short apophyses, and the two others with long, 

 and of these Plioladidea has prickly ridges in the fore part, and 

 Pholas is prickly all over. Pholas, it will be found, has four species, 

 one of which, dactylics, has four shields, the others having one, and 

 of these Candida has radiating ribs, parva transverse ribs, and crisp at a 

 longitudinal ribs. Pholadidea has only one species, and that has two 

 dorsal shields, so that the prickliness is not the only guide. 



One more bivalve. Its pallial line is not indented, its shell is 

 equivalve, it has no ears, and it has many teeth. This stops us 

 early. If the hinge is straight, the genus is Area-, but the hinge is 

 curved, then it is either Pectunculus, Leda, or Nucula. The shell is 

 practically circular and the teeth are in two groups, one on each 

 side of the beak ; that is the sign of Pectunculus and no other. 

 Pectunculus it is, and turning to the species we find there is only one, 

 glycimeris, and that the genus belongs to the Arcadae, which in their 

 turn belong to the Filibranchiates, of which we have only three 

 families Anomiidae, Arcadae, and Mytilidas. These three are 

 strangely unlike : the Mytilidae being the mussels, the Anomiidae 

 being the oyster-like mollusc with the large hole in the under valve 

 through which the byssus passes, and the Arcadse being made up 

 of Area, Pectunculus, and Limopsis, all of which have the many- 

 toothed hinge. 



Now let us take a gastropod, and let it be a fair-sized specimen 

 with plenty of ribs and striations. Look at its mouth : is there any 



