PELECTPODA 



573 



Fig. 901 

 Crenella 

 glandula 

 (Verrill). 



C. glandula (Totten) (Fig. 901). Shell 12 mm. long, 9 mm. high, 

 7 mm. wide, brownish-yellow in color: New Jersey to Gulf of St. Law- 

 rence, in shallow water. 



5. LITHOPHAGTTS Bolten (Lithodomus Cuvier) . Shell cy- 

 lindrical, inflated, rounded in front, wedge-shaped behind : 

 4 species on the South Atlantic and 1 on the Pacific coast. 



L. lithophagus (L.) (Fig. 

 902). Shell elongate, 3 to 8 

 cm, long, with fine longitu- 

 dinal and transverse lines: Florida; West 

 Indies; Europe; it attaches itself to a 

 rock by its byssus when young, into which 

 it bores when adult, forming a hole the 

 shape of the shell. It made the holes in 

 the columns of the Temple of Serapis 

 at Puzzuoli in Italy, which are used as 

 proofs of the oscillations of the coast in 

 that region. 



Fig. 902 



us lithophagus 

 (Rogers). 



ORDER 3. PSEUDOLAMELLIBRANCHIATA. 



The consecutive filamentous leaflets of each row of the gills are 

 more or less connected, and the two limbs of each leaflet are joined 

 by interfilamentary partitions (Fig. 890, C) ; the ascending limb also of 

 the outer leaflet is united with the mantle, except in Pectinidae; foot 

 weak or absent ; genital and kidney pores distinct except in the Pectinidae; 

 but 1 adductor muscle, the anterior usually being very small or absent; 

 mantle entirely open, with no siphons : 4 families, all marine. 



Key to the families of Pseudolamellibranchiata here described: 



! Two adductor muscles, the anterior one very small 1. AVICULIDAE 



cr a But one adductor muscle. 



&! Shell irregular ; oysters 2. OSTREIDAE 



6 2 Shell regular ; scallops 3. PECTINIDAE 



FAMILY 1. AVICULIDAE. 



Shell usually with valves of unequal size, the right valve being 

 smaller; animal rests on the right valve and is attached by its byssus: 

 numerous species, in tropical and temperate seas; about 6 species on the 

 Atlantic coast, all towards the south. The pearl oyster, Meleagrina 

 margaritifera (L.), which attains a length of 30 cm. and lives in the Indian 

 Ocean in 6 to 15 fathoms, belongs to this family. A closely allied 

 species of the same genus in the West Indian waters also furnishes 

 pearls. 



