128 THERSITES. 



having a long duct ; containing sections Thersites, Glyptorhagada, 

 Badistes, Sphcerospira, Hadra. 



Subgenus RHAGADA, with small, depressed globose shell, calca- 

 reous in texture and white or whitish, often multilineate ; the anat- 

 omy as in the preceding. 



Subgenus XANTHOMELON, with a globular shell with wide colum- 

 ellar lip, the spermatheca duct short. 



Subgenus THERSITES Pfr. 

 Section Thersites Pfr. (restricted). 



Thersites PFR. (in part), Mai. Blatter ii, p. 141 (1855 or 1856). 

 v. MARTENS in Alb., Die Hel. p. 157, type H. richmondiana. PILS- 

 BRY, Man. Conch, vi, p. 90. Cf. HEDLEY, Proc. Roy. Soc. Queens, 

 v, p. 62, and vi, 1889, p. 62, pi. 3 (anatomy). Not Thersites Spence 

 Bate 1857 (Amphipoda), nor Pagenstecher 1861 (Entomostraca). 



Shell lens-shaped or trochiform, imperforate when adult, carinated 

 at the periphery, more or less pinched at the keel, the last whorl de- 

 scending in front. Aperture sub-triangular, oblique, the outer lip 

 expanded, sinuous above the outer angle ; basal and columellar lips- 

 reflexed. Type T. richmondiana Pfr., pi. 29, fig. 8. 



Animal externally like Sphcerospira. Jaw strongly arcuate, with 

 slightly attenuated, blunt ends, sculptured with about 11 flat ribs, 

 broader than their interspaces, and denticulating the cutting mar- 

 gin (pi. 34, fig. 7, T. richmondiana). Radula as in Sphcerospira. 



Genitalia (pi. 33, fig. 1, T. richmondiana) as in Sphcerospira mit- 

 chellce, etc. The penis is short and dilated distally, evidently for the 

 accommodation of an internal papilla. Epiphallus long, bearing the 

 retractor at its middle, terminating in a short flagellum. Duct of 

 spermatheca very long, its lower portion large and swollen. 



As will be seen by the figures, the anatomy of Thersites richmond- 

 iana offers no departure of more than specific value from that of 

 Sphcerospira mitchellce and its allies. The group is simply a keeled 

 form of Hadra, really not more different from the normal Hadras 

 than Polygyra (Stenotrema~) spinosa is from P. stenotrema, or than 

 Chlorcea thermites is from C. sirena. The development of a keel is 

 now universally acknowledged to be a character of very slight sys- 

 tematic value in the Helices, too slight in most cases to be held of 

 more than specific importance. Scores of sectional groups contain 

 both rounded and keeled species. The true relationships of Thersites 



