POLLICIPES SERTUS. 329 



Carina, triangular, internally deeply concave, either 

 straight, and with the apex free, or inwardly and con- 

 siderably curved ; basal margin nearly straight. 



Rostrum, about half the length of the carina; either 

 straight or inwardly curved ; it projects freely for full half 

 its length ; inner growing surface triangular, more than 

 twice as high as wide ; basal margin very slightly hollowed 

 out. The sitb-carina and sub-rostrum are larger than 

 the largest of the latera ; their inner surfaces are trans- 

 versely elongated, rounded at both ends, and slightly 

 concave j externally they are pointed, and project out- 

 wards ; sometimes the sub-carina, and sometimes the 

 sub-rostrum is the largest. 



Latera, small, with their inner surfaces transversely 

 elongated, the larger being the most elongated. Externally 

 they are acuminated, and directed upwards ; they project 

 but very little beyond the thick membrane in which they 

 are imbedded. Neither the number, size, nor shape of 

 the latera agree on opposite sides of the same individual ; 

 and it would appear that, occasionally, some of them cease 

 to grow, and disappear. In the large specimen with only 

 thirty-one valves, the three pairs of latera, corresponding to 

 the upper, rostral, and carina! latera in Scalpellum, were 

 larger in a marked manner than the others ; but in the 

 specimen with fifty-four valves, this could hardly be said 

 to be the case. In this latter specimen, some of the valves 

 in the lowermost whorl were exceedingly minute. 



Peduncle, broad, about as long as the capitulum ; 

 surface of attachment wide ; calcareous scales minute, 

 placed in transverse rows, which become less and less 

 regular in the lower part. The scales do not stand very 

 close together ; they are of unequal sizes and irregular 

 outline ; generally spindle-shaped ; calcareous matter is 

 added regularly only to the scales in the uppermost row, 

 and irregularly to some of the lower scales. The latter, con- 

 sequently, are the largest, and often much elongated ; they 

 are sometimes of singular and irregular shapes. 



Colour. — The membrane covering the valves and 



