KEY TO UROCOPTIIXE. XXxiii 



bifid. Shell slender, slowly tapering, with hollow axis 

 and entire spire, the protoconch smooth. 



Epirobia, xv, p. 59. 



II. Radula of the ordinary shape, the teeth arranged in 

 nearly straight transverse rows (pi. 14, figs. 5, 10) ; cen- 

 tral teeth narrower than the laterals, and notably differ- 

 ent in shape; lateral teeth crowded, oblique, with the 

 mesocone long and narrow, the ectocone small; marginals 

 differing only in the increased size of the ectocone, and 

 more normal shape of the tooth. Jaw high-arched, very 

 thin, composed of many narrow plaits, converging to form 

 a triangular area of short plaits in the middle (pi. 14, 

 fig. 4). MICROCERAMIN^E. Microceramus, xvi, p. 151. 



III. Eadula with teeth arranged in oblique, v-shaped, trans- 

 verse rows, the central tooth narrower and very unlike 

 the lateral teeth in shape ; laterals with broad mesocones 

 widely separated from the ectocones. Jaw thin, narrow- 

 plaited, plaits converging, leaving a triangular area of 

 short plaits in the middle. UROCOPTIN^:. 



a. Cusps with the cutting edges rounded and even. 

 &. Side teeth all of essentially the same shape (ex- 

 cept the rudimentary outermost ones), gradually 

 decreasing in size outwardly, or the third tooth 

 abruptly smaller; all with the ectocone well devel- 

 oped, though smaller than the mesocone (vol. xv, 

 pi. 60, 61). Urocoptis. 



c. Central tooth of the radula very narrow, its cusp 

 much narrower than the ectocones of the lat- 

 eral teeth. 



d. Axis of the shell slender and straight or 

 nearly so. 

 e. Shell small, diam. 4.5 mm. or less. 



Sect. Bactrocoptis, xv, p. 143. 

 e 1 . Shell stout, larger. 



Sect. Urocoptis, xv, p. 121. 

 d l . Lower half of the axis thickened, more or 

 less twisted; shell rather large. 



Sect. Spirocoptis, xv, p. 114. 



