248 PROCEEDINGS OP THE ACADEMY OP [1893. 



acter as in the true marginals. Sometimes in the fourth, and even 

 in the third tooth, the ectodont, though essentially simple, is finely 

 double-pointed, and in the same longitudinal rows single- and 

 double-pointed ectodonts may be seen irregularly alternating. The 

 sixth, though a marginal in its configuration, still makes the transi- 

 tion, sometimes having an indication of a plate reaching beyond the 

 reflection, and bearing only two outer cusps, rather short and a pro- 

 longation distal-ward with room for additional cusps, of which there 

 is sometimes just a trace in the form of a very short blunt fourth one. 

 The true marginals show 5-6 cusps, moderately long, in the 7th- 

 9th, the mesial one being somewhat longer than the second, 

 and slightly directed inward. The 12th tooth, like the following, is 

 a fine transverse bar, only finely serrate, while the 13th or last, 

 generally shows hardly a trace of cusps. 



One example showed a peculiar feature of the radula: At the 

 front end, for about 15 transverse rows, the cusps' were worn off 

 almost entirely by rasping, as usual (comjmre fig. G, PI. VIII), but 

 here the cusps of the last few rows were less so than the others. For 

 this there can be no explanation but that after a period of com- 

 parative rest one of greater activity followed. 



The following dimensions of the radula were found in several 

 fresh individuals, as well as in those treated with alkali : length 

 0"68-0"71, width 0*24 mm.; length of transverse row about - 01 

 mm. 



A younger specimen, of about 1*5 mm. diam., had the radula 

 with 60 transverse rows of 23 teeth, the first 3 on either side being 

 perfect laterals, the fifth a marginal, with only 2 or 3 small distal 

 cusps. The last 4 marginals are wide and thin transverse bars, 

 with quite small cusps, the last with none at all. 



The striation of the shell is somewhat unequal while quite fine 

 and irregular over the most part of the whorls, it is stronger and 

 rather regular at the umbilicus, and also at the suture ; here the 

 stria? appear, under the microscope, like ribs, about O'Oo-O'OSS mm. 

 apart. 



Westerlund says in his diagnosis (I. c.) of the present species : 

 " distinctly angular at the groove-like deepened suture." It made 

 the same impression on me ; but after examining numerous exam- 

 ples in different stages of growth, it was found that the whorls are 

 equally rounded to the very suture, and that the apparent angle 

 was an illusion caused by the reflection of the light. 



