440 



MOLLUSCA 



PHYLUM VI 



Section B. Taxodonta Neiimayr (emeiid.). 

 Superfamily 1. NUCULACEA. 



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

 or porcellanous with tuhuliferous external prismatic layer ; area ohscure, 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 



erous ; marine. 



Family 8. Otenodontidae Dali. 



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

 external, alivincular, without an external resilium ; pallial line simple. Ordovician 

 and Siluriaii. 



Gtenodonta Salter {Tellinomya Hall p.p.) (Fig. 652). Oval, smooth or con- 

 centrically striate, in the later horizons sometimes with Leda-like 

 ornamentation. Ordovician and Siluriaii. 



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

 hinge line and a radial buttress to the anterior addnctor. Silurian. 



p^^^ g^2 Family 9. Nuculidae Adams.i 



ctenodontapectun- Shell Compact, closed, with the teeth in two series meetinq below the 



culoidesHall. Ordo- , ,77777 ,777 



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



^^^^^^ 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 Recent. 



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

 reticulately sculptured. Silurian to Recent. Re- a 



presented by over 200 fossil and half as many Recent 

 species. 



Acila Adams. With divaricate sculpture. Lower 

 Cretaceous to Recent. 



Ohio. 2/j 

 Hall). 



Family 10, Ledidae Adams.i 



Shell as in the Nuculidae, but elongated with the 

 ligament variable, the resilium sometimes external or 

 absent, the internal shell layer sub-nacreous or por- 

 cellanous, the ends of the shell partly gaping ; the 



mantle lobes more or less united 



elongate siphons 



to Recent. 



Fi(i. 053. 

 A, Nucula strigilata Goldf. Upper 

 Trias; St. Cassian, Tyrol. i/i- B, N. 

 nucleus Linii. Miocene ; Grussbach, near 

 Vionna. i/j. 



ivith complete, sometimes 

 pallial line usually sinuated. Ordovician 



Gleidophorus Hall {Adranaria Mun.-Chalm.) (Fig. 

 654). Shell rostrate, the anterior side sh orter, with an 

 internal radial buttress. Ordovician and Devonian. 



Gytherodon Hall. Silurian and Devonian. (?) Redonia 

 Rouault ; Gadomia Tromelin ; Palaeoneilo Hall ; Anuscula 

 Barr. ; and Myoplusia Neiimayr. Silurian. 



Fio. 654. 



CkidopTiorus cuUratus Sandb. 

 Internal monld from Lower Devon- 

 ian ; Niederlahnstein, Nassau, i/j. 



1 Verrül, A. E., and Bush, K. ./., Revision of the genera of Ledidae and Nuculidae. 

 Joura. Sei. [4], 1897, vol. iii. 



Am er. 



