POLLICIPES. 59 



mens, consisting of a scutum, terga, carinse, and upper latera ; and to Mr. F. E. Edwards 

 the loan of several very perfect specimens. 



Valves ; smooth, rather thin. Scutum (fig. 8, e) elongated, very slightly convex, many- 

 sided, almost oval, with its upper point produced, but apparently apt to be broken off. 

 Occludent margin slightly arched ; basal margin consists of two sides, of which the rostral 

 side is extremely oblique to the other, the two sides together forming a very large angle 

 with the occludent margin ; the tergo-lateral margin also consists of two sides, meeting 

 each other at a very open angle ; the lower half forms above a rectangle with the basal 

 margin ; possibly this lower half corresponds with the widely-truncated baso-lateral angle 

 in P. dorsatns, and with the smaller similar angle in the tertiary P. carinatus. A faint 

 rounded ridge runs from the apex to the baso-lateral angle, and thus divides the valve into 

 two nearly equal halves. Internally there is a deep pit for the adductor muscle ; only a 

 narrow internal edge along both sides of the apex is marked by lines of growth. 



Terga (fig. 8, d) ; elongated, rhomboidal, flat and thin ; carinal margin continuously 

 curved ; apex much produced ; the occludent and upper carinal margins meet each 

 other at much less than a right angle ; occludent margin slightly longer than the scutal 

 margin, which latter in the upper part is very slightly hollowed out ; a faint, rather wide 

 ridge, runs down the centre of the valve to the rectangularly-pointed basal angle ; a small 

 portion of the upper part of the terga projected freely. 



Carina (fig. 8, a, b, c) ; narrow, with the lower part somewhat spear-shaped ; almost 

 straight, transversely convex, with the central part forming a broad rounded crest ; lateral 

 margin a little inflected ; basal margin extraordinarily produced, with its apex square ; 

 internally, the corium-covered surface is produced upwards into the sharpest apex; a 

 small portion only of the uppermost part of the valve projected freely. 



Upper Latera (fig. 8, /) ; flat, almost pentagonal, with the two upper margins consider- 

 ably longer than the three lower ones ; of these three, the carinal margin is the shortest, and 

 the other two equal, with the rostral one considerably arched or convex ; these three basal 

 margins must have been in contact with the Latera of the lower whorl ; the apex did not 

 project freely. I have not seen any latera of the lower whorl, but Mr. Sowerby gives 

 figures of some minute valves, which no doubt were such. Several of Mr. Edwards's speci- 

 mens are tinged a pale-reddish purple. 



Dimensions. The valves described are all rather small ; the largest, a tergum, is a httle 

 more than a quarter of an inch in length. 



Affinities. This species is more nearly related to the section of the genus containing the 

 recent P. cornucopia, elegans, and polymerus, than to the other sections. Its affinity is 

 closest to P. cornucopia, though in the form of the basal margin of the scuta there is more 

 resemblance to P. polymerus. The scutum presents some points of resemblance to the 

 cretaceous P. gracilis and dorsatus. 



