440 



MOLLUSCA 



PHYLUM VI 



Pig. 652. 



Section B. Taxodonta Neumayr (emend.). 



Superfamily 1. NUCULACEA. 



Shell of variable form, closed ventrally, equivalve, loith a smooth epidermis ; nacreous 

 or porcellanous iviih tubuliferous external prismatic layer ; area obscure, or none, when 

 present divided into lunule and escutcheon ; ligament variable, amphidetic ; gills folio- 

 branchiate ; both adductors present and sub- equal ; foot grooved and reptary, not 

 byssiferous ; marine. 



Family 8. Ctenodontidae Dall. 



Shell nuculiform, with the teeth in a continuous arched series ; no area ; ligament 

 external, alivincular, icithout an external resilimn ; pallial line simple. Ordovician 

 and Silurian. 



Ctenodonta Salter (Tellinomya Hall p.p.) (Fig. 652). Oval, smootli or con- 

 centrically striate, iii^ the later horizons sometimes with Leda-like 

 ornamentation. Ordovician and Silurian. 



Gucullella (M'Coy) Fischer. Ovate, thin-shelled, with a straighter 

 hinge Hue and a radial buttress to the anterior adductor. Silurian. 



Family 9. Nuculidae Adams.^ 

 ctenodonta pectim- Shell compact, closed, with the teeth in two series meeting below the 



culoidcs HaXl. Ordo- , ,77777 .71, j, 



vician; Cincinnati, umbones, separated by a chondrophore ; area represented by an obscure 

 H^m ^'^ ^^^^^^ lunule and escutcheon ; no ligament, but a wholly internal, amphidetic, 

 alivincular resilium ; internal layer of shell nacreous; mantle lobes 

 free, without siphons ; pallial line simple. Silurian to Eecent. 



Nucula Lam. {Nuculana Link) (Fig. 653). Oval or triangular, concentrically or 

 reticulately sculptured. Silurian to Eecent. Re- a 



presented by over 200 fossil and half as many Recent , r!^^Z"~^. c 



sj)ecies. 



Acila Adams. With divaricate sculpture. Lower 

 Cretaceous to Recent. 



Family 10. Ledidae Adauis.i 



Shell as in the Nuculidae, but clungated icith the /^"".,V ^ ,,. 7, 



... ,. . 7 A, Nucula stngilata Goldf. Upper 



ligament variable, the resihum sometimes external or Trias ; St. Cassian, Tyrol. Vi- f-, n. 



absent, the internal shell layer sub-nacreous or por- ^J^^^^l Linn. Mioceno; Gru.ssbaeh, near 



cellanous, the ends of the shell iiartly gaping; the 



mantle lobes more or less united ; with complete, sometimes 

 elongate siphons ; pallial line usually satiated. Ordovician 

 to Recent. 



Gleidophorus Hall (Adranaria Muu. -Chalm.) (Fig. 



654). Shell rostrate, the anterior side shorter, with an 



internal radial buttress. Ordovician and Devonian. 



^"■- 654. Gytherodon Hall. Silurian and Devonian. (?) Bedonia 



Ckidirplwrus ruUrat^ s,u„ll>. Rouault ; Cadomia Tromelin; Palaeoneilo Hall; Anuscula 

 Internal iiKinkl iroHi Lower Devon- . ' 



ian ; Nieiieriahnstoin, Nassau. V,. Barr. ; and AlyojAusia Neiimayr. Sihuiau. 



^ Vemll, A. E., and BksIi, K. ,/., Revision of the genera of Ledidae and Ninulidae. Anier. 

 Jouni. Sci. [4], 1897, vol. iii. 



