LAMELLIBRANCHIATA. 



in front ; body of the penultimate whorl bearing an indistinct tubercle 

 above, and, near the columella, a compressed plait, scarcely descend- 

 ing ; columella plait simple, slightly ascending ; peristome white 

 or rose coloured, inflated externally, with the margins united by a 

 very thin deposit ; right margin furnished within with a longitudinal 

 crest, which, above the middle, is interrupted by a semicircular notch ; 

 columella margin much dilated, spreading. Length, 1 ; breadth, - 7.~ 

 (Pfei/er.) 



Singapore and Pulo Penang. 



Sub-order Operculata. 

 Furnished with an operculum. 



FAMILY AMPULLACERID^;. 



Shell spiral, globular, umbilicated. 

 Marine or estuarine. 



AMPHIBOLA. 



Globular, surface uneven ; columella fissured ; outer lip channelled 

 near the suture ; operculum horny, sub-spiral. 

 Australia. Pacific Islands. 



270. A. avellana, GmeMn ; Gray, Die/. N.Z., ii., p. 248. Sub- 

 orbicular, rather thick ; whorls angled and flattened behind, trans- 

 versely rugosely plicate ; spire very short. Yellowish or reddish 

 brown, generally more or less purple on the spire and keel ; interior 

 brownish purple; inouth white. Axis, '8 ; breadth, '95. 



Class Lamellibranehiata. 



No head, nor eyes ; shell composed of two valves, occasionally with 

 supernumerary pieces ; heart with two chambers ; nervous system with 

 three principal pairs of ganglia. 



ORDER PHOLADACEA. 



Mantle closed, but allowing two more or less elongated siphons to 

 pass out, which are contiguous at the base ; the inferior with two 

 pairs of branchiae. 



PHOLADID^l. 



Shell gaping at both ends, thin, white, brittle ; hinge plate reflected 

 over the umboues, and a long curved muscular process beneath each ; 

 anterior muscular impression on the hinge plate ; pallial sinus very 

 deep. 



Boring holes in wood and rocks. 



