PLATE XXVII. 



Fig. 345. Heterofusus retroversus ; from an original drawing by Mr. Alex. 

 Agassiz. 



h. heart, d. c. digestive cavity. op. operculum. m. mouth. a. anus. 

 ov. ovary. s. siphon. w. wings. t. tentacle, ot. otolite. 



Fig. 346. The same, at rest on the bottom of the jar. 



Fig. 347. The same, in rapid motion ; the natural position of this figure is sacri- 

 ficed to the exigencies of the plate, the shell should be much less ob- 

 liquely poised, and the upper arm should be nearly horizontal. 



Fig. 348. The same, floating with expanded arms, as seen from the top of the 

 jar, when the animal is in captivity. 



Fig. 349. Heterofusus balea. The shell, copied from Dr. Stimpson's figure 

 of Spirialis Qouldii. 



