17 1 PROCEEDINGS OF THE NATIONAL UUSEl I/. vol.38. 



bulb can be pushed forward, but even this could hardly produce Mich 

 forms as figured by Bergh. 



Jaws. -(PI. 22, figs. 2, 3, 4.) The mouth opens into a narrow tube 

 of oval section, thin walled, and running between the two jaws which 

 arch it over and also partly inclose its sides. The jaws are of brown 

 chit in, thin and delicate, about twice as long as high, serrate on their 

 lower edges, the serrations growing coarser from posterior to anterior. 

 Each jaw is molded to lit along the top and one side of the mouth 

 tube, narrows to a rounded point posteriorly and appears to be squarely 

 and smoothly cul oil' anteriorly: but about this last there may be some 

 doubt since there is a suspicion that in removing these delicate objects 

 from the tough mouth gristles, serrations or other structures at the 

 point of attachment may have been broken off and lost. To the 

 powers of the dissecting microscope the jaws appear covered with 

 beautifully regular minute transverse (i. e., dorso- ventral) striations 

 corresponding in spacing with the serrations of the ventral edge. 

 The real microscopic structure was not studied. There can be little 

 doubt it is substantially that several times figured by Ber<;h for simi- 

 lar objects, i. e.. a sort of mosaic of minute chitinous bars locked 

 together in a diamond pattern which gives the impression of trans- 

 verse (i. e., dorso- ventral) lines, the longitudinal (i. e., anteropos- 

 terior) lines being broken in the pattern. 



Pharyngeal bulb and radula. (PI. 22, figs. 2, 3, 5, 6.) Near the pos- 

 terior end of the jaws the thin-walled mouth tube suddenly swells to 

 more than twice its former diameter to contain the large muscular 

 pharyngeal bulb. The structure of this was not minutely studied as 

 it offered no prospect of material difference from the similar organs so 

 often and fully elucidated by Bergh Its form sufficiently appears from 

 the figures and must in life vary greatly in t he course of the complicated 

 mi >t ions of the radula which latter, however, in this species I think is 

 almost certainly not prot rusible. I think so, both because the mouth 

 and end of the snout are too small and because there is a pretty clear 

 mutual adjustment of the radula and jaws to trituration of the food 

 between them in the swollen portion of the mouth tube. The radula 

 commences posteriorly in a bulb borne on a Ionic stem which is a pro- 

 longation of the posterior base of the pharyngeal bulb but rises sharply 

 upward and to the left, penetrates the dorsal wall of the mouth 

 tube, then curls over forward and outward and lies on top of the 

 mouth tube at its widesl part to the left of it- center. The radula, 

 starting in this bulb, passes down through it- stem and so into the 

 lower posterior part of the pharyngeal bulb, through which it then 

 turns sharply upward, reaching its surface (and so coming into use in 

 the open mouth-cavity) at the highest point of the bulb's top. At 

 the same point the radula attain- its own greatesl width, for by wear- 

 ing off of the lateral members and by .-oppression it thence slightly 

 narrow- a- il run- forward down the anterior slope of the pharyngeal 



