TROCHUS. 515 



whorl, which causes the basal outline to appear submargi- 

 nated and bluntly subangular. In certain of the southern 

 examples, the angular character of the shell becomes almost 

 entirely lost, and these individuals entirely agree with the 

 specimens of Rackettii forwarded to us by Dr. Philippi. 



The aperture is squarish, and broader than it is high ; 

 the length in general is not equal to that of the spire, the 

 breadth is equal to, or rather exceeds, half the basal 

 diameter. There is no particular sculpture ; the nacre is 

 generally brilliant ; the outer lip is acute ; the pillar lip 

 rather oblique, straightish, a little incurved above, gene- 

 rally reflected there, and sometimes so much so as par- 

 tially to conceal the small but profound umbilicus, the 

 mouth of which latter is smooth, large, and abrupt. Our 

 largest specimen (a Shetland one) measures four lines and 

 a half in length, and the same at the base. 



The animal is of a white or yellowish white hue, 

 speckled with black or lead-coloured markings. Its muzzle 

 is rather broad, finely crenated at its edges, and is marked 

 with dark transverse lines. The tentacles are setaceous, 

 white, and (as well as the lateral filaments) as if finely 

 frosted, being covered with fine cilia. The eye-peduncles 

 are white, the eyes dark. The head-lobes are rather large 

 and even. The neck-lappets have even edges and are 

 white. The sides of the foot are more or less mottled and 

 streaked with dusky colouring. The disk of the foot is 

 oval, rounded in front and obtuse behind. 



In the curious variety (?) from the Zetland seas, de- 

 scribed in the 19tli volume of the "Annals of Natural 

 History" as a form of Margarita undidata, the markings 

 of the foot are brownish, the foot itself angulated in front, 

 and the tentacles more subulate and much more strongly 

 ciliated. These characters would seem to indicate specific 



