18 



COMPARATIVE ANATOMY 



CHAP. 



Sub-Order 2. Tellinacese. 



Diniyarian with completely separate siphons. Foot large. Gills smooth. Fam. 

 Tellinidse (Tcllina). Fam. Donacidse (Donax), Mactridse (Martm). 



Sub-Order 3. Veneracea. 



Dimyariau with somewhat folded branchial lamella?.. Siphons separate, and foot 

 large. Fain. Veneridae (/"/*!, Aft'trtrix [C>jthe>vf<~\, Tapes). Fam. Petricolidse : 

 boring muscles. 



Sub-Order 4. Cardiacea. 



Dimyariau or Monomyarian. Branchial lamella? much folded. Mantle closed 

 except at the two siphonal and one pedal apertures. Fam. Cardiidse : Dimyarian. 



710, 



Fa;. -JO. Anatomy of Cardium tuberculatum, h-ft aspect (after Grobben, Leuckart, and 

 Nitsche, Zonl. n'miJtufeln). ji, Foot ; ijo, gonad ; S, shell ; Pa, mantle ; os, labial palps ; o, month; 

 -l/i, anterior adductor muscle; a 1 , oesophagus; m, stomach; I, digestive gland; </, intestinal 

 canal ; 300, genital aperture ; /"<i, pericardia! aperture of the kidney ; V, ventricle. ; At, auricle ; /', 

 pericardium ; no, aperture of the kidney in the mantle cavity ; n, kidney ; jl/o, posterior adductor ; 

 Bl, point of concrescence of the right and left ctenidia behind the foot ; a, anus ; At;, anal chamber 

 of the mantle cavity, with anal siphon ^ls ; l!k, branchial chamber of the same cavity with 

 branchial siphon Bs ', Br, ctenidium. 



(Cardinal [Fig. 26].) Fam. Cbamidse : Dimyarian. Valves of shell unequal. ( 



Jt'i'ijii.ii'ittit.) To these the fossil forms MmmpJ, //,/'/", C<tprini<la. Hip- 

 Huil inl it iiii<_\ Fam. Tridacnidse : ilonomyarian. (Tridacna, ffippopus.) 



Sub-Order 5. Myacea. 



Diniyarian with folded branchial lamella. Tendency towards concrescence of the 

 edges of the mantle folds. Siphons very long and foot large. Fam. Psammobiidae : 



pedal cleft of the mantle still 



large (Pxuiinii<A>i<i'\ Fam. Mesodesmatidse. 



