LITHOTRYA TRUNCATA. 367 



Scuta locked into a deep fold in the terga: carina 

 with a prominent central rounded ridge in the upper part : 

 rostrum and latera rudimentary, about ^th of the width of 

 the carina. 



Mandibles, with nearly three times as many pectina- 

 tions between the first and second teeth, as between the 

 second and third teeth ; distauce between the tips of the 

 first and second teeth equal to that between the tip of 

 the second tooth and inferior angle. Maxillae widely 

 notched, with the inferior part forming two prominences. 

 Caudal appendages shorter than, or barely exceeding in 

 length, the pedicels of the sixth cirrus. 



Friendly Archipelago, Mus. Paris ; Philippine Archipelago, Mus. Cuming ; 

 imbedded in coral rock. 



Capitulum rather thick, with the five main valves 

 having their free apices, diverging and truncated. The 

 upper and old layers of shell do not here scale off so 

 readily as in many of the foregoing species ; and hence an 

 unusually large proportional length of each valve pro- 

 jects freely above the sack ; and the valves are of unusual 

 thickness. The capitulum is very nearly as wide at its 

 summit as at its base, owing to the divergence of the 

 apices of the valves. The scuta and terga are articulated 

 together by a conspicuous fold, which, when seen from 

 vertically above, (PL IX, fig. 1 a',) appears like a deep 

 wedge-formed notch in the terga. On the exterior sur- 

 faces of the valves, the teeth on the successive rims are 

 approximate ; on the inner surfaces, the rims are covered 

 by strong yellow membrane, which is generally fringed 

 with small horny spines. 



Scuta, exterior surface convex, sub-triangular, with the 

 apex truncated : seen vertically from above, there is a 

 small rectangular indentation or fold which receives the 

 projecting scutal margin of the terga. The inner growing 

 or corium-covered surface (fig. 1 5, b') is triangular, with its 

 tergal margin largely hollowed out. Along the occludent 

 margin there is a slight ridge, which terminates at the 



