ORDER III TELEODESMACEA 393 
anterior and posterior laterals in the right valve only. Plectodon, Carp. ; surface granulated. 
Rhinoclama, D. and S. ; like Plectodon, but without cardinal teeth. Tropidomya, 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. Lwzonia, Dall. Tertiary and Recent. 
Myonera, Dall and Smith. Shell thin with concentric waves and sparse radial 
ribs ; hinge edentulous ; rostrum short, rounded. Recent, abyssal. 
? Corburella, Lycett. Middle Jura. Spheniopsis, Sandberger. Tertiary. 
Order 3. THLEODESMACBHEA. Dall. 
A. PANTODONTA. 
Laterals exceeding two in any one group. 
Family 1. Allodesmidae. Dall. (Cycloconchidae, Ulrich). 
Shell rounded ; valves equal, free, closed, with feeble concentric sculpture; area 
linear, amphidetic ; ligament sub-external, parivincular, opisthodetic ; adductor scars 
sub-equal, pedal scars above and distinct from the adductors ; pallial line entire ; hinge 
with 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. 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 multiplication 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 7'e/eodesmacea only as a probable ancestor, rather 
than a perfectly developed type of the modern assemblage. 
Orthodontiscus, Meek (Oycloconcha, Miller; ? Anodontopsis, M‘Coy). Silurian ; 
Ohio. 
Allodesma, 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. DrIoGENODONTA. 
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 obscwre. 
Family 2. Pleurophoridae. Dall. 
Shell substance cellulo-crystalline ; 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 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. Devonian to Recent. 
l Cyprinidae, p.p. of authors, but this name cannot be used. 
