DIOTOCARDIA — RHIPIDOGLOSSA 



407 



which become successively obliterated; through these holes, the 

 posterior of which is anal, pass tentacular appendages of the 



mantle ; no operculum. Cretaceous . Single genus, ^aZ/o^/s; 



principal sub-genera PadoUus, Teinotis. 



Fam. 3. Pleurotomariidae. — Central tooth single, narrow, 

 about 26 laterals, 60 to 70 uncini. Shell generally variously 

 trochiform, nacreous, operculate, with a rather broad marginal 

 sinus in the last whorl ; as this sinus closes up it forms an " anal 

 fasciole " or " sinus band." Cambrian 



-. Principal genera: 

 Scissurella, epipodial line with several long ciliated appendages at 

 each side, shell very small, slit open, sinus band extending nearly 

 to apex ; Scliismope^ anal slit closed in the adult into an oblong 

 perforation; Murcliisonia (Palaeozoic only), shell long, turreted, 

 whorls angulate or keeled with a sinus band ; Odontomaria 

 (Palaeozoic only), shell 

 tubular, curved ; Polytre- 

 maria (Carboniferous), 

 shell turbinate, slit a series 

 of small holes connected 

 by a passage ; Trochotoma^ 

 shell trochiform, perfora- 

 tion consisting of two nar- 

 row holes united by a slit ; 

 Pleurotomaria^ branchiae 

 almost symmetrical, radula 

 as above, shell variously 

 spiral. 



In Pleurotomaria we 

 have the case of a genus 

 long supposed to be extinct. 

 More than 1100 fossil 



species have been described, and within the last 38 years about 

 20 specimens, belonging to 5 species, have been discovered in 

 a living state. 



Fam. 4. Bellerophontidae. — Shell nautiloid, spire generally 

 concealed, aperture large, sinus or perforations central (Fig. 179, 

 p. 266). Ordovician — Trias. Genera: Bellerophon, Trema- 

 tonotus, Cyrtolites. 



Section II. Azygobranchiata. — One ctenidium (the 

 left) present. 



Fig. 269. • 



Pleurotomaria adansonianaCx. and 

 F., Tobago. X I 



