66 TONICELLA. 



be several in number. The sinus is very wide and very spongy 

 (fig. 33) ; the sutural laminse are high and narrow. 



The girdle is somewhat sparsely clothed with blunt white processes, 

 between spines and scales in form, and some of them show under the 

 lens an excessively fine longitudinal striation (fig. 30.) 



Gills extending forward two-thirds the length of the foot. 



The length is about 6 mill. ; divergence 90°-100°. 



Aleutian Is. 



Views of outside and interior of a median valve, and interior of 

 the head valve are here given. The pores of the eaves and sinus are 

 obviously more than sufficient to afford egress to the minute trunks 

 innervating the megalsesthetes and micrsesthetes ; and they probably 

 serve in large part for the attachment of the valves to the girdle, being 

 occupied by connective tissue. This accessory means of attachment 

 is perhaps the cause of the great degeneration of the insertion- plates, 

 which are deprived of their main function. 



Trachyradsia multidentata Cpr., from the Bonin Is., is evidently 

 closely allied, but it is described as having more strongly developed 

 teeth. 



Genus TONICELLA Carpenter. 



Vide vol. xiv, p. 40. 



Toniciella Thiele, Das Gebiss der Schnecken ii, p. 389. 



Key to sjiccies of Tonicella. 



a. Shell small, less than 10 mill, long; central areas red, lateral 

 areas white, saccharina. 



aa. Shell larger, much variegated. 



b. Speckled and maculated with red ; minutely granulated ; 

 dorsal angle 90°-100°, marmorea, vol. xiv, p. 41. 



bb. Having oblique reddish lines ; dorsal angle 110°-130.° 

 c. Very minutely granulated; angle 120°-130°, 



suhmarmorea, vol. xiv, p. 42. 

 cc. Not granulated; angle 110°-125°, lineata, vol. xiv, p. 42. 



T. saccharina Dall. PI. 15, figs. 22, 23, 24. 



See vol. xiv, p. 44. 



Figures are here given of a curled specimen, kindly supplied by 

 Dr. W. H. Dall. The girdle is blackish and smooth outside, having 

 a fringe of delicate spicules at the edge, which is curled up in the spec- 



