256 THE LAMELLIBRANCHIA 
ligament internal (Figs. 200, 230). Malletia, Des Moulins ; the ligament 
external, Nuculina, d’Orbigny. Famity 4. Crenopontipar, Wohr- 
mann. An extinct family from the Silurian; the shell is nuculiform 
and the hinge presents an uninterrupted arcuate row of teeth. Genera— 
Ctenodonta, Salter. Cuculella, Fischer. Cardiolaria, Meunier-Chalmas. 
The fossil group Palaeoconcha, Neumayr, is connected with the 
Protobranchia through the Solenomyidae. It contains the following 
families, all of which are extinct :—Famity 1. PRancarDmDAE, Neumayr 
Shell equivalve, with the hinge dentition of Arca. _Genus—Praecardium, 
Barrande ; from the Silurian and Devonian. Famiry 2. ANTIPLEURIDAER, 
Neumayr. Shell inequivalve ; the hinge with an obscure resemblance to 
that of Arca. Genus — Antipleura, Barrande; from the Silurian. 
FaMILy 3. CARDIOLIDAE, Neumayr. Shell equivalve and ventricose ; the 
hinge without teeth. Genus—Cardiola, Broderip ; from the Silurian and 
Devonian. Faminy 4. GrRaMMysIIDAE, Fischer. Shell thin, equivalve, 
Fig. 231. 
Solenomya togata, Poli, left-side view (the left pallial lobe and gill cut away). a, anus; ad’, 
ad”, anterior and posterior adductor ; ao, aorta; a.or, anal orifice of the mantle; au, heart- 
auricle ; c.g, cerebral ganglion ; f, foot; je, foot elevator ; fp, foot protractor ; fr’, fi”, anterior 
and posterior foot retractor ; g, right gill; hy.g, hypobranchial gland; k, kidney ; m, mouth ; 
pa, mantle; pe, pericardium ; p.g, pedal ganglion ; p./, palp appendage ; pl.g, pleural ganglion ; 
7.0, renal opening ; st, stomach; v, heart-ventricle ; vi.c, visceral commissure ; vi.g, visceral 
ganglion. 
oval, or elongate, the cardinal border thickened but without teeth. 
Genera — Grammysia, Verneuil; from the Silurian and Devonian. 
Protomya, Hall, from the Devonian, Cardiomorpha, de Koninck ; from 
the Silurian to the Carboniferous. Famimy 5, VuastipAr, Neumayr. 
Shell thin, very inequivalve, the hinge without teeth. Genus—Vasta, 
Barrande; from the Silurian. FamIny 6. SoLENOPSIDAE, Neumayr. Shell 
equivalve, thin, greatly elongated, the umbones very far forward. 
Genus—Solenopsis, MacCoy, from the Devonian to the Trias. 
ORDER 2. Filibranchia. 
These are Lamellibranchs whose main character is the possession 
of gills formed of parallel, ventrally directed, and reflected filaments. 
The successive filaments are joined together by cilia disposed in 
“ciliated discs” (Figs. 210, A; 232, fy). The foot is generally 
