SCAPHOPODA. Vii 



The radula (pi. 39, figi. 8, 9) is short, nearly rigid and curved, 

 and incapable of being used as a rasping organ as in other mollusks. 

 Its function is probably largely as a crushing plate, like the " giz- 

 zard-plates " of Tectibranchs. 



The dentition of the Scaphopoda, so far as known, does not show 

 great diversity. The formula of teeth is 1.1.1.1.1. The median 

 tooth is always a nearly flat plate, which in Dentalium is much 

 wider than long, in Entalina is but little wider than 'long, and in 

 Cadulus and Siphonodentalium is longer than wide. The single 

 lateral on each side has an erect, rather shovel-shaped cusp, with 

 several denticles. In Dentalium these denticles are short and in- 

 conspicuous ; in the other genera Entalina, Siphonodentalium and 

 Cadulus there are two or three stout and distinct denticles. The 

 uncini, one on each side, are trapezoidal flat plates, thickened to- 

 ward their inner edges. 



Dentalium. No species of the typical group or subgenus has been 

 examined anatomically. In the subgenus Antalis the dentition of 

 vulgare (tarentinum), entails and occidental (" striolata " Sars) is 

 known. See pi. 39, fig. 6, D. occidentale Stimp. 



In Fissidentalium the radulae of D. megathyris, plurifissuratum 

 and magnificum have been examined, and are said to agree with 

 Antalis. In Ehabdus I find some divergence in the laterals, the cusp 

 being rather strongly bidentate (pi. 39, fig. 5, D. rectius Cpr.). 



It will be noticed that with the exception of the species last men- 

 tioned, the forms yet examined belong to two very closely allied 

 subgenera. When some of the more divergent groups, such as 

 Bathoxiphus, Episiplion and Fustiaria, are examined, it is likely 

 that further modifications will be found. The examination of some 

 species of Compressidens is especially to be desired, as that group 

 may prove to belong to the Siphonodentaliidce, in which case it will 

 probably be ranked as a subgenus of Siphonodentalium. 



Entalina. The teeth of E. quinquangularis have been examined 

 by G. O. Sars (pi. 39, fig. 10). The rhachidian teeth are wider than 

 in other known Siphonodentaliidce, but narrower than in Dentalium. 

 The laterals are strongly dentate. 



Siphonodentalium. G. O. Sars has figured the radulae of S. lo- 

 batum (vitreum') and S. lofatense. The rhachidian teeth are as long 

 as wide or longer, and somewhat pentagonal. Laterals strongly 

 tridentate. PI. 39, figs. 7, 8, 9, S. lobatum. 



Cadulus. The dentition of C. propinquus is figured by G. 0. Sars 

 (pi. 39, fig. 11). It is similar to that of Siphonodentalium. For 



