470 ■ MOLLUSCA phylum vi 



anterior and posterior laterals in the right valve only. Plectodon Carp. ; surface granulated. 

 Rhinoclama D. and S. ; like Plectodon, but without cardinal teeth. J'ropidomya D. and 

 S. ; hinge witli a buttress, one anterior cardinal, but no lateral in either valve. Halonymplia 

 D. and S. ; right valve with a single cardinal, no other teeth in either valve, a conspicuous 

 posterior laminar buttress in each valve. Luzonia Dali. Tertiary and Recent. 



Myonera Dali and Smith. Shell thin with concentric waves and sparse radial 

 ribs ; hinge edentulous ; rostrum short, rounded. Recent, abyssal. 



(?) Gorhurella Lycett. Middle Jura. Spheniopsis Sandberger. Tertiary. 



Order 3. TELBODBSMACEA DaU. 



A. Pantodonta. 

 Laterals exceeding tivo in any one group. 



Family 1. Allodesmidae Dali {Gycloconchidae Ulrich). 



Shell rounded; valves equal, free, closed, with feehle concentric sculpture ; area 

 linear, amphidetic ; ligament suh-external, parivincular, opisthodetic ; adductor scars 

 suh-equal, pedal scars ahove and distinct from the adductors ; pallial line entire ; hinge 

 with one or two lateral laminae on each side of the beaJc, the posterior helow the ligament, 

 received into corresponding grooves on the right valve; cardinal teeth radially grooved ; 

 one or two in each valve, those in the right valve stronger. Ordovician and Silurian. 



This family, as suggested by Neumayr, probably exemplifies the first step in the develop- 

 naent of the Teleodesmacean hinge. But it must be adraitted that its amphidetic though 

 linear area, the occasional multiplication to three of the lateral laminae, and the sub-ligament- 

 ary localion of the hinder laminae, are very reminiscent of the prevalent Silurian Schizodont 

 type, and the family can be adraitted to the Teleodesmacea only as a probable ancestor, rather 

 than a perfectly developed type of the modern assemblage. 



Orthodontiscus Meek {Cycloconcha Miller ; (?) Anodontopsis M'Coy). Ordovician 

 and Silurian. 



Ällodesma Ulrich. Like Orthodontiscus, but more elongate, the beaks more 

 anterior, the anterior adductor scar buttressed by a radial ridge, and the anterior 

 lateral teeth short or absent. Ordovician 



B. DiOGENODONTA. 



Laterals normally one or two, and cardinals three or less, in any one group. 



Superfamily 1. CYPEICARDIACEA Dali. 



Lobes of the mantle partly closed ventrally ; anterior lateral laminae absent, or 

 grouped with the cardinal teeth, short and obscure. 



Family 2. Pleurophoridae DalLi 



Shell substance cellulo-cry stalline ; valves equal,free, closed ; adductor scars sub-equal, 

 free from the pedal scars ; pallial line entire, or feebly sinuated ; area obscure ; liga- 

 ment external or seated in a groove, parivincular ; margins of the valves usually piain ; 

 hinge with one left and two right posterior laminae, the anterior laminae absent or con- 

 fused with the cardinals ; two or three cardinal teeth in each valve, of which the posterior 

 in both valves is sub-parallel to the dorsal shell margin, and in the right valve is usually 

 bifid. Mantle with a moderate pedal and two siphonal openings, the latter usually not 

 produced into tubes. Devonian to Recent. 



1 Cyprinidae p.p. of authors, but this name cannot be used. 



