MOLLUSCA. GASTEROPODA 247 



Mitra. Shell fusiform, thick. Spire elevated, summit acute. 

 Aperture narrow, elongate, notched in front. Columella with 

 several oblique folds, of which the posterior are the stronger ; 

 outer lip not reflected, thickened, but not grooved internally. No 

 operculum. Eocene to present day. Ex. M. episcopalis, Recent ; 

 M. (Mitreola) labratula, Bracklesham Beds. 



Voluta. Shell thick, ovate, with short spire and turbinate 

 protoconch. Last whorl very large ; on the posterior part are 

 nodules or spines which are continued anteriorly as transverse 

 (or axial) ribs. Aperture elongate, with an angular channel at 

 the posterior end ; broad, and deeply notched at the anterior end ; 

 outer lip thick ; inner lip with thin callus. Columella with several 

 transverse, only slightly oblique folds, of which the four or five 

 anterior are strong and nearly equal, and the posterior two or three 

 are smaller. Eocene to present day. Ex. V. musica, Recent ; 

 V. 7iuisicalis, Eocene. 



Vollltospina. Shell fusiform, with rather short, conical 

 spire ; protoconch small, with sharp apex. Last whorl very large, 

 tapering anteriorly. Whorls step-like, owing to the posterior part 

 being flattened or concave ; at the angle of the whorls is a row 

 of spines (usually prominent) which are prolonged anteriorly as 

 transverse (or axial) ribs ; the latter are usually crossed by spiral 

 ridges. Aperture elongate ; at the posterior end one channel at 

 the suture, another at the level of the row of spines ; anteriorly 

 the aperture is truncated and slightly notched. Outer lip usually 

 thin ; inner lip with thin callus. Columella with four or five very 

 oblique folds, of which the anterior are stronger than the posterior. 

 Upper Cretaceous to present day. Ex. F. spi/wsa, Eocene ; V. 

 luctatrix, Barton Beds. 



Ancilla ( = Ancillaria). Shell smooth, oval or oblong; last 

 whorl large ; sutures usually covered by callus. Aperture elongate, 

 broadening anteriorly, with a small notch near the suture, and 

 a deep sinuosity at the anterior end which is truncated ; columella 

 with callus posteriorly, twisted, and with folds anteriorly. Creta- 

 ceous to present day. Ex. A. buccinoides, Bracklesham, Barton, and 

 Headon Beds ; A. cinnamonea, Recent. 



Pleurotoma. Shell turreted, fusiform, spire long and sharp, 

 last whorl long. Aperture oval, elongate ; outer lip curved, with 



