1920.] 



B, Prashad : Notes on Lamellihranchs. 



167 



opposed in the young, becoming depressed and less marked in 

 older specimens ; sculptured with numerous low corrugated ridges 

 arising from an eccentrically situated nucleus, and radiating out- 

 wards on the two sides but more or less parallel in the middle region ; 

 a few very minute striae also run transversely in this region. 

 Older specimens with the beak much eroded and bleached and 

 showing barely any striations. Shells swollen in the middle but 

 depressed in front, below and behind. Periostracum coarse, with 

 strong vertical ridges in the young radiating outwards, some with 

 a well marked V-shaped course. In adult shells the striations less 

 marked but distinct ; a few minute transverse concentric ridges 



I'iG. I. — Arcidopsis footei (Theobald). 



A. Hinge of the left valve of adult specimen, XiL 



B. Hinges and scars of the young specimen, X2. 



also visible in both young and adults ; regions of growth well 

 marked. Periostracum of a yellowish brown colour with a few 

 light green striae along the vertical striae, specially distinct in the 

 young specimens. Nacre pearly white, iridescent. Hinge strongly 

 developed ; pseudocardinals three in the right valve with the 

 middle tooth best developed, two in the left, the outer being much 

 the larger ; all these teeth verticall}' striate in adult shells. Later- 

 als lamellar, nearl}^ straight, one in the right, two in the left valve, 

 in which the lower ridge is better developed, being longer and 

 stouter than the upper. Muscular scars moderately impressed ; 

 anterior scars confluent, posterior scars distinct. PaHial line dis- 

 tinct though not deeply marked. 



