484 PROCEEDINGS OF THE VATIONAL MUSEUM. vol.38. 



Fig. 7. Marsenina prodita. Shell. (This and next two figures arc drawn, regardless 

 of scale, for comparison of shell structure, forming a progressive degenera- 

 tion series.) 



8. Marsenina ampla . Shell. See remarks under fig. 7. 



9. Onchidiopsis corys. Shell, represented semidiagrammatically as a solid object, 



from below. Sec remarks under lit:. 7. 

 10. Onchidiopsis corys. Osphradium and ctenidium, semidiagrammatically rep- 

 resented froman anterior viewpoint . C7.=ctenidium; />. = dorsal; L.=left ; 

 Os.=osphradium; R.=right; l'.=ventral. The Btippling represents the 

 black-piemen ted areas on the roof of the gill cavity and basal surfaces of 

 the lobes of the osphradial leaflets. 



Plate 22. 



Fig. 1. Onchidiopsis corys. Dorsal view of head region. Notaeum is slightly slit up 

 from inspiratory deft and the lobes of the anterior lappet turned back. 

 ah. e.=abnormal eye; ah. £.=abnormal (external) branch of the bifid left 

 tentacle; 6.=foot; e.=eye;/.=auriele of foot ; g. c.=opening of gill cavity; 

 I. L=left lobe of anterior lappet; /. /. = left tentacle; p. oas. = penis, basal 

 portion; p. cr.=penis, crest; r.=rostrum; r. /.=right lobe of anterior Lappet; 

 r. <.=right tentacle. 



2. Dissection of rostrum. Dorsal view. h. m.=buccal mass; /.= jaws; I. £.=left 



tentacle; ph. = wall ol pharynx; ph. car. = pharyngeal cavity; r.=rostrum; 

 ratf. =radula; rad. s«c.=radula sac; re. ?».=rctractor muscles; /\/. = right 

 tentacle. (The walls of the dorsal half of the rostrum are represented 

 as cleanly cut away except at the tip, which is intact. The retractor 

 muscle bundles, which line it, are only partially shown, and some are 

 represented as broken and pushed aside to allow a view of the pharynx. 

 The thin-walled pharynx is represented as partially transparent, and 

 through it, represented in dotted lines, are seen the jaws and the buccal 

 mass, the latter containing the greater portion of the radula. On top of the 

 pharynx and to the left lies the radula sac. a prolongation of the buccal 

 mass the neck of which pierces the pharynx wall. The radula is shown 

 as if the radula sac and buccal mass were semitransparent . > 



3. Semidiagrammatie view of rostrum from left Bide. The wall of the rostrum 



is supposed to be wholly removed except at the tip, where it is intact. A.8 

 in the last figure, the jaws and buccal mass are represented a- seen through 

 the thin-walled pharynx, and the radula as if -ecu inside the buccal 

 mass and radula sac; but in this figure their lines are not dotted, bettering 

 as in last ; also, ///. mouth. 

 •1. Jaws, seen from left side. . 1 . =anterior; Z).=dorsal; P.=posterior; K=ven- 

 tral. 



5. Radula. Dorsal view of three rows from near broadest point (about ten rows 



from anterior end i. Camera bifida drawing. X oc. L, obj.3. 



6. Radula. Two uncinal hooks from right side. Camera lucida drawing. 



X oc. 1, obj. 7. 



Plate 21, figures I, 2, 3, and in, and Plate 22, all figures, were drawn by the author 



from the specimen. Plate 21, figure- I. •">, and C, were, drawn b\ Mr. Sergius Morgulis, 

 from the specimen Plate 21, figures 7 and 8, are copied from figures reproduced in 

 Tryon's Manual of Conchology. 



