THYSANOPHORA. 55 



Euclasta Lederer, Verb. Zool.-bot. Vereinsin Wein, v, p. 252, 1855, 

 and Weiner Eritom. Monatschr. vii, p. 423, 1863 (Microlepido- 

 ptera). 



Shell varying from flat and discoidal to depressed-globose and to 

 conical or pyramidal ; thin; pale brown, yellow or corneous, some- 

 ivhat translucent or at least not opaque; narrowly umbilicated ; sur- 

 face rather dull, smooth or with slender riblets (generally cuticular), 

 or densely, minutely bristly. Embryonic whorl not distinctly 

 demarked from the after-growth, smooth or granular. Whorls 4- 

 65-, convex, separated by deep sutures, the last whorl rounded or car- 

 inated. Aperture lunate or oblong ; lip thin, simple or a trifle 

 expanded, the columellar margin more or less dilated. Type T. 

 conspurcatella Morel., pi. 16, fig. 3. (See also pi. 16, fig. 4, T. 

 cceca. PL 16, figs. 5, 6, 7, T. hypolepta. PI. 16, figs. 8, 9, 10, T. stig- 

 matica. PI. 16, figs. 1, 2, T. turbiniformis). 



Foot (of T. peraffinis} narrow, the sole not tripartite ; upper sur- 

 face granulated, the tail having a median sulcus above (pi. 15, fig. 

 8), sides granulated, with oblique grooves but no distinctly differ- 

 entiated foot-margin (fig. 9). Tail without mucus pore. 



Genital system unknown, but oviduct (of T. peraffinis} containing 

 several hard and brittle-shelled white eggs. T. vortex has been 

 observed by Morse to be viviparous. In this genus, therefore, as in 

 Sagda, both viviparous and oviparous species occur. 



Jaw thin and delicate, flexible, strongly arcuate, composed of many 

 flat, narrow lamellae, the free edges of which appear as vertical striae ; 

 lower margin of jaw denticulated by the lamellae (pi. 15, fig. 7, T. 

 peraffinis. PI. 15, fig. 6, T. turbiniformis}. 



Dentition : Rhachidian tooth with square basal-plate and three 

 stout cusps, the mesocone projecting beyond the basal-plate. Lateral 

 teeth bicuspid, the entocone completely absent. Marginal teeth 

 various in form ; having either (1) a long oblique mesocone, and a 

 small simple or bifid ectocone ( T. peraffinis pi. 15, fig. 10, and also 

 T. incrustata, T. ingersolli*) ; or (2) the mesocone is bifid by union 

 with the entocone (T. turbiniformis pi. 15, fig. 5, and also T. granum, 

 T. vortex, T. pubescens}. In T. granum, incrustata and vortex the 

 ectocone is trifid ; in the others it is either simple or bifid. 



The jaws and teeth of turbiniformis and pubescens, and the teeth 

 of T. cceca have been figured by W. G. Binney, Ann. N. Y. Acad. 

 Sci. iii, pp. 105, 106, 113; those of T. incrustata, T. iiiyersolli and T. 



