MOLLUSCA OF INDIA. 75 



dorsal iobe. The right dorsal lobe (fig. 6) is of the ordinary form 

 and ample, the left (fig. 6 a) in two very distinct portions ; the 

 posterior does not extend far back. 



The jaw (Plate LXXXI. fig. 1 e) has no central projection on the 

 cutting-edge. 



The radula (figs. 1-1 d) is very long and very broad, 8*5 x 4 mm., 

 there being a greater number of large central teeth than usual. They 

 are straight-sided teeth, elongately triangular in form, all of equal 

 size, two intermediate of less breadth, succeeded by long narrow 

 curved uoicuspid teeth. At about the 70th tooth from the central one 

 a slight notch becomes apparent near the apex, which soon develops 

 in the marginal teeth into the bicuspid form, and about twenty of the 

 outermost are very small. The arrangement of the teeth is : — 



125 . 2 . 20 . 1 . 20 . 2 . 125 

 147 . 1 . 147 

 295 in the row. 



I counted 163 rows, or some 48,000 teeth. 



Generative organs (Plate LXXX. fig. 6 b). The retractor muscle 

 of the penis is situated at about three fourths of tho total length of 

 the long tube-like sheath from the generative aperture up to the 

 terminal bulbous point where the vas deferens is given off; there is 

 thus no free kalk-sac, as in Macrochlamys and Oxytes. The ama- 

 torial organ is very large, solid, and cylindrical, with a retractor 

 muscle. The spermatophore is pear-shaped and short. The oviduct, 

 albumen-gland, &c. present no characteristic features. 



It may be noticed that the form of the mantle-lobes is somewhat 

 like those in Macrochlamys, but there the resemblance ends ; the 

 radula differs completely both in the number and form of the teeth, 

 being, as regards the larger straight laterals, like those of O.vytes. 

 The generative organs of Uemiplecta differ from both. Of all the 

 species that have hitherto been described in full, it agrees in a most 

 interesting and complete way with lihysota cymatkim from Penang. 

 This is described by Stoliczka in a paper on the shells of that place, 

 J. A. S. B. 1873, p. 11 ; the right and left shell-lobes are present, 

 and we find the same large number of teeth in each row ; the only 

 difference noticeable is the small size of the central tooth in 

 cymatium. These characters remove it from lihysota, which 

 Semper clearly points out has (1) no shell-lobes to the mantle, and 

 (2) the simple form of the genital organs, the amatorial organ being 

 absent in all the species he describes. I do not myself place much 

 value on the polished lower surface of the shell as a generic 

 character. Shell-lobes have no invariable connection with a 

 polished glassy surface, for in many species of true Macrochlamys 

 possessing very lengthened shell-lobes they play over a rough 

 decussated shell-surface — notably M. cleciissata of the Khasi Hills. 

 lihysota cymatium must be transferred to Hemiplecta. So also must 

 clensa (Plate LXXXI. figs. 2-2 c). My description of the animal of 

 this fine species from Borneo, published in the P. Z. S. Jan. 6, 1891, 



