DIOTOCARDIA — RHIPIDOGLOSSA 



407 



which l)OcomG successively ohliterated ; through these holes, the 

 posterior of which is anal, pass tentacular appendages of the 



mantle ; no operculum. Cretaceous . Single genus, Haliotis ; 



principal sub-genera Fadollas, Teinolls. 



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

 al)0ut 26 laterals, GO to 70 uncini. Shell generally variously 

 trocliiform, nacreous, opercidate, with a rather broad marginal 

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



fasciole " or " sinus band." Cand)rian . Principal genera : 



Seissurrlla, epipodial line with several long ciliated ap})endages at 

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

 to apex ; Schismopc, anal slit closed in the adult into an oblong 

 perforation; Murchisonia (Palaeozoic only), shell long, turretted, 

 whorls angulate or keeled with a sinus Ijand ; Odontomaria 

 (Palaeozoic only), shell 

 tubular, curved ; Pohjtrc- 

 maria (Carboniferous), 

 shell turbinate, slit a series 

 of snudl holes connected 

 l)y a passage ; Troclwtoina , 

 shell trocliiform, perfora- 

 tion consisting of two nar- 

 row holes united by a slit ; 

 Pleurotomaria, branchiat; 

 almost symmetrical, radula 

 as above, shell variousl}' 

 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 al;)Out 

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

 living state. 



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

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

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

 tonotus, Cyrtolites. 



Section II. — Azygobranchiata. — One ctenidium (the left) 

 present. 



Fig. 269. 



Pleurotomaria adansoniana Cr. ami F., 

 Tobago. X i. 



