no. 1761. I \/:U" SPECIES 01 < > \ < ' II I I > K U'sl s i:\l.< II. 475 



hull), ending abruptly shortly after passing within the jaws. It 

 attains a length of 60 transverse rows and is typically taenioglossate, 

 having the usual formula 2-1-1 1 2. The median or rhachidian 

 tooth consists of a base about as wide as high, with slightly convex 

 lower edge and concave sides, the top of which curls over backward 

 to form the dentate functional blade. The latter bears a large central 

 cusp, long and pointed, flanked by very irregular and much smaller 

 denticulations, about eight on each side but varying from six to ten 

 and showing a distinct tendency to alternation of larger and smaller. 

 The whole tooth is arched, with the convexity posterior, so that the 

 functional upper portion as seen from on top has a roughly crescent ie 

 form. The laterals, or ad-medians, are on the same general plan, but 

 the basal portion is much narrower and higher, the central (or sub- 

 central) cusp longer in proportion and flanked by about seven denticu- 

 lations on the external and five on the internal side. They are set on 

 the basal membrane at an angle with the rhachis, so that the central 

 cusps point slightly inward. The uncini have the form of simple 

 smooth arched claws, curving upward, backward, and slightly out- 

 ward. By folding inward over the admedians they can be laid flat. 

 Possibly they can also be folded outward. The radula presents only 

 minute differences from the other species of the genus so far as 

 comparison with figures shows. 



Foot.— (PI. 21, figs. 2, 3; PI. 22, fig. 1.) Moderate in size, as before 

 described, anteriorly slightly bowed and concave, posteriorly obtusely 

 pointed. The anterior angles form distinct stout lobes or auricles. 

 The posterior portion, projecting beyond the notseum border, is some- 

 what specialized, being slightly broader and thicker than at the point 

 where it passes beneath the notaaun, and curled sharply upw ard. This 

 might be thought to be a mere accident of preservation in this speci- 

 men, but has been described for other species of the genus. Whether 

 it occurs in life or is due to the strong contraction in death of the 

 structure next mentioned is uncertain. The dorsal surface of the 

 foot is appressed to the edge of the notseum where it passes beneath 

 it, and at and posterior to this point bears a narrow central muscular 

 thickening or pad. Similar structures have been minutely described 

 by Bergh for other species of the genus. The function is unknown 

 but does not its position suggest that it max be merely a vestigial 

 operculiferous lobe '. 



Parasites. On sectioning the left tentacle two large encysted 

 parasites were found, complex organisms, probably Trematodes. 

 Prof. Henry B. Ward, of the University of Illinois, is kindly examin- 

 ing them and it is hoped to present further conclusions in connection 

 with the forthcoming paper in the American Naturalist. 'Die high!} 

 abnormal character of this tentacle and its parasitization may possi 

 bly be more than a coincidence. Nematodes have been found with 

 the larvae of O. <jm nhun/im (Bergh [1887], p. 276, note). 



