286 Notes on Lingual Dentition of Mollusca. 



melampiis bidentatiis, Say. 

 The specimen which furnished the lingual membrane figured 

 was collected at Newport, R. I., by Mr. Sam. Powel. 



Fig. 7. 



Lingual dentition of Melanipus bidentatus, Say. 



Lingual membrane broad. ' Teeth 33.1.33. Centrals small, 

 upright, with rounding base and bulging sides, reminding one 

 somewhat of the ace of clubs, its apex elongated, terminating in 

 a distinct, acute denticle ; this central is attached to a very large 

 triangular plate, greatly expanded above. Laterals uniform, 

 larger than the centrals, of the same shape, but less symmetrical, 

 and with a much more extended and narrower basal projection ; 

 these laterals are perpendicular, but are attached to obliquely 

 curving plates, long and narrow, each plate being detached. 

 There are about thirteen of these laterals, in almost straight hori- 

 zontal lines, on both sides of the median line. The nncini change 

 abruptly from the laterals, are in oblique rows, are attached to 

 upright, oblong plates, square at top and base, diminishing as they 

 pass off laterally ; the uncini are rather square, their broad, simple 

 apices are armed with three strong deoticles, the inner denticle 

 being the largest. 



The figure represents two rows of centrals with the laterals to 

 the right of the median line and a few uncini. The upper line of 

 figures gives the central, the first two laterals, one of the uncini, 

 and one of the laterals in profile, all detached. 



The teeth of this membrane are so nearly on a plane as to allow 

 one photograph to bring out all the details. 



