470 MOLLUSCA phylum vi 



anterior and posterior Laterals in the right valve only. Plcctodon Carp. ; surface granulated. 

 Rhinoclama 1). and S. ; like Plcctodon, but without cardinal teeth. I'rojndomya D. and 

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

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

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



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

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



(?) Corburella Lycett. Middle Jura. Siihenio-psis Sandl^erger. Tertiary. 



Order 3. TELEODESMACEA Dall. 



A. Pantodonta. 

 Laterals exceeding two in any one group. 



Family 1. Allodesnaidae Dall (CtjcloconcJiidae Ulrich). 



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

 linear, am^^hidetic ; ligament sub-external, 2>arivincular, opisthodetic ; adductor scours 

 sub-equal, pedal scars above and distinct from the adductors ; pallial line entire ; hinge 

 ivith one or two lateral laminae on each side of the beak, the posterior below 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- 

 ment of the Teleodesmacean hinge. But it must be admitted that its amphidetic though 

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

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

 type, and the family can be admitted to the Teleodesmacea only as a probable ancestor, ratiier 

 than a perfectly developed type of the modern assemblage. 



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

 and Silurian. 



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

 anterior, the anterior adductor scar l)uttressed 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. CYPRICARDIACEA Dall. 



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

 grouped with the cardinal teeth, short and obscure. 



Family 2. Pleurophoridae Dall.^ 



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

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

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

 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, l^evonian to Recent. 



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



