56 THYSANOPHORA. 



vortex in Terr. Moll, v, p. 170-173, and Man. Amer. L. Sh., p. 356. 

 The jaws and teeth of T. perdepressa and T. peraffinis have been 

 examined by myself. All of these species have essentially the same 

 type of jaw. The teeth vary only in the denticulation of the mar- 

 ginals, as noted above. The jaw is distinctly stegognathous in type, 

 being more like that of Flammulina than that of Pyramidula. 



The absence of a parapodial groove widely sunders this genus 

 from Pyramidula, Cfiaropa, Phasis and Amphidoxa. The first of 

 these groups differs also in the structure of the jaw. Thysanophora 

 agrees with Hyalosagda in characters of the jaw, dentition, foot and 

 the calcareous-shelled eggs. 



The shell of Thysanophora somewhat resembles that of Pyrami- 

 dula ; but it is less opaque, never flame-painted nor strongly rib- 

 striate. The columella moreover is generally dilated as in Trachy- 

 cystis. 



The species inhabit the Greater Antilles, with a few in Bermuda, 

 Florida and the Gulf States, and extending to the Middle American 

 mainland from Vera Cruz and Yucatan south to Trinidad. The 

 forms from the periphery of this area are small or minute, but in 

 the large West Indian islands species of considerable size occur. 

 These snails live upon the ground, under leaves or stones. 



More than any other group of Antillean Helices, the Sagda-Thy- 

 sanophora-Zaphysema group impresses us as being an original West 

 Indian element. The other main genera of the Antilles, Pleurodonte 

 and Hemitrochus, with the allies of each, show far-reaching affinities 

 with Old world Helices ; and Polygyra has been derived from the 

 North American fauna ; but not only is the Sagda-Thysanophora- 

 Zaphysema group characteristic of the Antillean region now, but no 

 Helices known to approach them in morphology of genitalia and 

 shell have been found in any other part of the world. Thus, as far 

 as present knowledge enables us to judge, of the three main stocks 

 into which the West Indian Helix fauna is sharply divided, the 

 Thysanophora, etc., phylum is that which has longest occupied the 

 region, and probably developed its peculiar features therein, arising 

 from some very early, un differentiated Helix stock of the Poly- 

 placognathous type. The other two great groups are much later 

 (although still ancient) elements, which reached the Antillean tract 

 after their essential anatomical features had become well estab- 

 lished. 



