60 SAGDA. 



haldemaniana andjayana by Binney. All agree with the descrip- 

 tion given above, and with those of S. similis and 8. cookiana 

 examined by the writer. 



The prominent features of the shell in this genus, are its Zonites- 

 like texture, the subvertical aperture, and sharp simple lip. The 

 genital system is peculiar for its appendix and flagellum on the 

 penis, and the long spermatheca duct. The teeth of the species 

 investigated agree in the long mesocones, constantly present ecto- 

 cones, and bicuspid marginals. The jaw in the typical forms is 

 smooth, by the complete union of its component laminae; in the 

 section Hyalosagda, which is nearer the ancestral stock, the jaw shows 

 vertical imbricating plates, as in Thysanophora, Flammulina, etc. 



The genus Sagda is by no means so isolated in the family of 

 Helices as has been supposed. Its relationship with Thysanophora 

 and especially with Zaphysema, is moderately intimate. 



The analogy of the shell of Sag da with that of the Zonitid genus 

 Gastrodonta is remarkable. Both contain forms with spiral internal 

 lamina?, and depressed forms without laminae ; the section Hyalo- 

 sagda being quite comparable to the section Zonitoides. Gastrodonta 

 too, has elevated forms (G. ligera, etc.) recalling Sagda in contour. 



Sagda is confined to the island of Jamaica, with the exception of 

 the subgenus Odontosagda inhabiting Haiti and Cuba. The 

 species and forms are numerous, extremely variable, and correspond- 

 ingly difficult to determine. This difficulty is enhanced by the fact 

 that some of the best specific characters can be seen only by break- 

 ing an opening in the last whorl a half volution behind the aperture ; 

 the vicinity of the suture being the best place for the incision. By 

 this means only may the form and length of the lamella? be observed, 

 as is the case with Plectopylis and some other groups. The lamella) 

 are present in young specimens, but are progressively absorbed as 

 the animal grows, so that in adults they do not extend inward much 

 beyond the last whorl. The basal lamina is sometimes totally 

 absent in species normally possessing it, just as in Gastrodonta ; but 

 as in that genus, it is a comparatively rare condition in most species. 



Subdivisions. 



Section Sagda (restricted). Shell imperforate, the axis solid; 

 aperture having a spiral lamina within the last whorl and generally 

 a fold on the columella. Type S. cookiana, pi. 16, figs. 11-13. (See 

 also pi. 16, figs. 16, 17, S. connectens, and pi. 16, figs. 14, 15, S. alligans.) 



