PLATE XT. 



Diagrammatic figures to illustrate the situation of the dorso-median medullary nerve, and at the same 

 time the arrangement of the dift'erent layers of the body-wall and their respective relation as to size, &c. 



The twelve upper figures are supposed to bo taken as transverse sections just above the proboscidian 

 sheath, and are on purpose aU reduced to the same scale, by which process the relative importance 

 of the integumentary layer is clearly brought out. 



The corresponding muscular layers are indicated by the same Greek letters — a is the most important 

 longitudinal one, common to all; ji, the circular; y, the outer longitudinal; S is a circular muscular 

 layer characteristic of the Carinellidai (figs. 1, 2, 3, 6, 13, and 14); it here forms the dorsal wall of the 

 proboscidian sheath and at the same time it forms part of the body-wall in the anterior part of the 

 body ; in all the others it has become detached and has possibly developed into the outer wall of the 

 proboscidian sheath, and as such is not indicated in figs. 5, 7-12. /, stands for the integument ; B, for 

 the primary basement membrane separating this from the muscles; h, for the secondary basement layer. 



The plexus and medullary nerve are indicated by a yellow tint. 



Fig. 1. Carimna grata, n. sp. 



Fig. 2. Garinina grata, n. sp. More posteriorly. 



Fig. 3. Curinella. 



Fig. 4. Carinetta. Further back in the region where the proboscidian sheath does not extend. 



Fig. 5. Cephalotlirix. 



Fig. 6. Carinoma armaiull (M'Int.), Oud. Here the proboscidian sheath nerve lies below the 

 medullary nerve and is thicker than the latter. 



Fig. 7. Carinoma annandi (M'Int.), Oud. Further backwards in the region where the jiro- 

 bosoidian .sheath does not extend. 



Fig. 8. Anqyliijiurus or Drepanopliorus. 



In figs. 9-12 the proboscidian sheath nerve is indicated and is seen to be less conspicuous than in 

 Carinoma. 



Fig. 9. Certbratntati corrugatus, M'Int. 



Fig. 10. Cerebratulun niedidlatuK, n. sp. The deeper glandular layer of the integument has 

 fused with the outer layer of longitudinal muscles, and the primary basement mem- 

 brane has thus disappeared. 



Fig. 11. Cerebratuliis macrorcn, n. sp. 



Fig. 1 2. Enpolia giardii, n. sj). 



The figs. 13-17 have reference to transverse sections of the body- wall in the region of the lateral 

 nerve-stem. 



Fig. 13. Carinetta (for Carinim, rf. PI. III. fig. 7). 



Fig. 14. Carinoma (innandi (^I'lnt.), (.'ud. 



Fig. 15. Ceiihulothrix. 



Fig. 16. Gerebratutus. 



Fig. 17. Amptiijiorii<. 



