344 Mr. E. A. Smith on a f^jecies o/"Fusus. 



Pulmonates approach much more nearly to the Opisthobrancha 

 than they do to the Prosobranchs ; we must therefore suppose 

 that they are derived from the former ; and it seems to me 

 that tliere are more reasons for uniting the Opisthobranchs 

 with the Puhiionates than with the Prosobranchs. The Gas- 

 tropoda would thus be divided into two subclasses. The 

 monoecious Gastropods {Gastropoda monoxa) would contain 

 the two orders Pulmdnata and Opisthobranchiata, while the 

 dioecious Gastropods [Gastropoda dioeca) would contain the 

 two orders Prosobranchiata and Heteropoda. 



EXPLANATION OF PLATE XV. 



Fig. 1. Sipltonariu australis : alimentary system, X 3. «, buccal mass ; 1>, 

 salivary glands; c, odontopbore ; d, beart ; e, stomacb;/, in- 

 testine ; y, liver ; h, rectum. 



Fig. 2. Reproductive system, X 3. a, penis ; h, vas deferens ; c, gland ; 

 d, ovo-testis ; e, bermapbrodite duct ; /, swollen portion of ovi- 

 duct ; g, albumen-gland ; h, narrow portion of oviduct ; /, sper- 

 matheca; />■, rectnm. 



Fig. 3. Animal witb tbe respiratory cavity laid open, X 2. a, bead ; b, 

 anus ; c, beart ; d, renal organ ; c, gill. 



Fig. 4. Portion of gill and balf tbe renal organ, X 10. d, renal organ ; 

 e,_gill. 



Fig. 5. Animal seen from below, x 2. «, foot ; b, bead ; c, respiratory 

 opening and lobe ; d, mantle. 



Fig. G. Nervous system, X 6. a, cepbalie ganglion ; h, pedal ganglion ; 

 c, parieto-splancbnic ganglia ; d, reproductive orifice. 



Fig. 7. Spermatopbore, X 12. 



Fig. 8. Mass of ova, nat. size. 



Fig. 9. Ovum witli embryo, X 160. 



Fig. 10. Ovum with embryo furtber advanced, X ICO. 



2^1^. 11. .Veliger of Siphonaria attsfralis, X 100. a, velum; b, otocyst j 

 c, foot ; d, opercuhun ; e, sbell ; f, retractor muscle. 



Fig. 12. Embryonic shell of Siphonaria austndis, X 160. 



XXXV. — Descrijytion of a Species o/'Fusus. 

 By Edgar A. Smith. 



Fusus corjpulentus. 



Shell large, ponderous, fusiform, uniformly light yellowish 

 brown, strongly spirally costate, striated and sulcate, lon^-i- 

 tudinally grooved on the upper whorls, and marked with strong 

 lines of growth on the rest of the surface. Volutions about 

 nine, sloping and very slightly concave at the upper half 

 convex below the middle, and somewhat constricted at the 

 base ; thickened above, just below the suture. Spiral ridges 



