364 LITHOTRYA RHODIOPTJS. 



Terga with the basal points narrow, and the carinal angle 

 produced. Rostrum and peduncle unknown. 



Mandibles, with four times as many pectinations 

 between the first and second main teeth, as between the 

 second and third ; distance greater between the tips of 

 the first and second teeth, than between the tip of the 

 second tooth and the inferior angle. Maxillae widely 

 notched, with the inferior part forming two obscure 

 prominences. 



Hab. unknown. Imbedded in a massive coral. Brit. Mus. 



The specimens are in a rather bad condition, and have 

 been disarticulated. They are of rather small size; the 

 rostrum and peduncle are lost, and animal's body much 

 injured. < 



Valves white, thin, translucent ; teeth on the projecting 

 rims small, narrow, standing further apart than their own 

 width. The upper layers have undergone but little dis- 

 integration or scaling off, and consequently the carina and 

 terga project freely. The valves, where not rubbed, are 

 covered by bright yellow membrane, which is thickly 

 clothed with rows of spines ; these are small on the 

 exterior surfaces, but are very large and hooked in certain 

 parts, as near the tergal margins of the scuta, and on the 

 carinal margins of the terga, and especially on the inner 

 face of the upper free part of the carina. Here the 

 hooked spines (fig. 4 d) are trifid or quadrifid, and are 

 very conspicuous. 



Scuta, as seen externally, triangular ; they overlap half 

 the width of the terga; on their internal faces (fig. 4#), 

 in the upper projecting part, there is a strong ridge, 

 against which the scutal margin of the terga abuts. There 

 is a deep and conspicuous pit for the adductor muscle. 



Terga, as seen externally, nearly triangular. The ridge 

 which leads from the apex to the basal angle, is rounded, 

 central, and extremely prominent ; but does not form a 

 furrow, or include the overlapping margin of the scuta. 

 The basal angle is narrow, spur-like, and slightly hollowed 



