CLASSIFICATION. XXXI 



d 2 . Compressed between convex and concave sides ; 



small, thin, rapidly tapering; no slit, notch or 



supplemental tube, Compressidens, p. 123. 



d 3 . Small, thin, fragile, smooth, very slender, but 



slightly tapering; acicular with simple or 



notched apex, or truncate with a supplemental 



apical tube, Episiphon, p. 117. 



d*. Without any of the foregoing combinations. 



e. Quite arcuate, glassy, with numerous low 

 variceal annular swellings,^! habdus,p. 11 2. 

 e l . Almost straight, glassy, smooth, thin, cir- 

 cular in section ; no slit or notch, 



Rhabdus, p. 112. 



e 2 . Arcuate, smooth or with growth-striae, sec- 

 tion circular or oval, apex slit or simple, 



Lcevidentalium, p. 97. 



e 3 . Smooth, but with longitudinal striae in the 

 young, lost with age in some specimens ; 

 see Section I, 



Antalis, p. 37 ; Graptacme, p. 85. 



Of the subgenera defined above, the following are known only as 

 fossils : 



Subgenus LOBANTALE Cossmann, 1889. 



Lobantale COSSM., Catal. Illustr. Coq. Foss. Eoc. Paris, in Ann. 

 Soc. Roy. Malac. Belg., xxiii, p. 7 (1889). 



Shell slender, compressed, smooth except for growth-lines, the in- 

 terior with two longitudinal ribs placed laterally, one on each side, 

 giving a transverse section a bilobed shape. Type D. duplex Defr. 

 (including the synonymous D. bicarinatum Desh.). PI. 39, figs. 12, 



Eocene, Paris Basin. No recent species known. A supplement- 

 ary apical pipe is sometimes developed, as in species of the group of 

 D.filum. In some Mesozoic and Palaeozoic forms, not allied to the 

 present group, there are also longitudinal ribs on the inside. 



Subgenus PLAGIOGLYPTA Pilsbry. 



Plagioglypta Pils., in Zittel's Text-book of Palaeontology, Ea&t- 

 man's edit., p. 



