ORDER I 



PRIONODESMACEA 





type of a distinct family, may also be included. It is distinguished by its feebler 

 structure ami a dorsal radial groove near the cardinal bonier. 



II. TAXODONTA. Neumayr (emend.) 

 Superfamily 1. NUCULACEA. 





Shell of variable form, closed veittrnlhf, njuii'iifrf, /'//// a *inootli / /"" rcous or 



porcellanous with t ubuliferous external prismatic layer ; area obscure, or none, when present 

 divided into lunule and escutcheon; ligament variable, amphiilttir : (fills 

 foliobranchiate; both adductors present and sub-equal; foot grooved ami 

 reptary, not byssiferous ; marine. 



I^imily 8 ? Ctenodontidae. Dall. 



Shell Nuculiform, with the, teeth in a continuous arched series ; no 

 area ; L ligament external, alivincular, without an external resiiimu : 

 pallial line simple^ Ordovician and Silurian. 



Ctenodonta, Salter (Tellinomya, Hall p.p.), (Fig. 603). Oval, smooth '^"'} 

 or concentrically striate, in the later horizons sometimes Ledaeform. Hall). 

 Ordovician and Silurian. 



Cucullella (M'Coy), Fischer. Ovate, thin-shelled, with a straighter hinge line and 

 a radial buttress to the anterior adductor. Silurian. 



Family 9. Nuculidae. Adams. 1 



Shell compact, closed, with tJie teeth in two series meeting below the 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, with nut 

 siphons ; pallial line simple. Ordovician to Recent. 



Nucula, Lam. (Nuculana, Link), (Fig. 604). 

 Oval or triangular, concentrically or reticulately 

 sculptured. Silurian to Recent. Represented by 

 FIG. 604. over 200 fossil and half as many recent species. 



A , Nucula stngiiata, Goidf. Upper Trias ; Acila, Adams. With divaricate sculpture. 



St. Cassian, Tyrol, l/,. B, N. nucleus, Linn. T 



Miocene ; Grussbach, near Vienna, i/,. Lower Cretaceous to Recent. 



Family 10. Ledidae. Adams. 1 



Shell as in the Nuculidae, but elongated with the ligament variable, the resilium sometimes 

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

 porcellanous, the ends of the shell partly gaping ; the mantle 

 lobes more or less united; with complete, sometimes elongate 

 siphons ; pallial line usually sinuated. Silurian to Recent. 



Cleidophorus, Hall (Adranaria, Mun. Chalrn.), (Fig. 

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

 internal radial buttress. Silurian and Devonian. 



Ci/therodon, Hall. Silurian and Devonian. ? Redonia, 

 Rouault ; Gadomia, Trornelin ; Tellinomya, Palaeoneilo, 

 Hall ; Anuscula, Barr. ; and Myoplusia, Neumayr. Silurian. 



Leda, Schum. (Figs. 606, 607). Shell rostrate, elongate, often keeled, concentri- 

 cally striate ; hinge as in Nucula ; pallial sinus small. Silurian to Recent. 



1 Verrill, A. E., and Bush, K. J., Revision of the genera of Ledidae and Nuculidae (Amer. Journ. 

 Science [4], vol. III. pp. 51-63), 1897. 



Fio. 005. 



drlilo/thorH* ruJti-iitiis, SandK 



