266 SCALPELLUM PERONII, 



upper portion produced into a flat projection ; this pro- 

 jection is almost spear-shaped, being constricted a little 

 on each side below the apex. There is a deep pit 

 for the adductor muscle. The umbo is near the apex, 

 the part above not being above one fifth of the whole 

 length of the valve. As in S. vidgare, the growth is at 

 first downwards, and subsequently a little upwards and 

 downwards, thus producing the upper, small, spear-like 

 projection, which lies at a lower level than the umbo. 

 There is a fold on the occludent margin. 



Terga, large, flat, triangular ; carinal margin slightly 

 hollowed out ; occludent margin slightly arched, with a 

 small portion protuberant to a variable amount. The 

 apex is slightly curved towards the carina. 



Carina, long, internally deeply concave, angularly bent, 

 the lower portion slightly longer and wider than the upper 

 part ; the two halves meet each other at about an angle 

 of 135°; the upper half is parallel to the longer axis of 

 the terga, between which it extends for three fourths of 

 their length. The external surface is rounded, except near 

 the umbo, where the edge is carinated ; growth almost 

 equally upwards and downwards ; the parietes and tectum 

 are not separated by ridges. 



The Sub-carina lies close under the carina, and is placed 

 almost transversely to the longer axis of the capitulum ; 

 external surface arched and smooth, the whole having the 

 shape of half of a cone, with the apex a little curved 

 outwards ; seen internally, it may be said to be formed 

 of two triangular wings placed at right angles to each 

 other ; basal margin straight ; in size equalling the 

 carinal latera. 



Rostrum, lying almost transversely to the longer axis 

 of the capitulum, under the basal margins of the scuta ; 

 in shape (fig. 6 a) closely resembling the sub-carina, but 

 about one third larger than it ; larger also than either the 

 rostral or carinal latera ; seen externally, appears like a half 

 cone ; seen internally, is formed of two triangular wings 

 (with curved edges), placed at right-angles to each other. 



