COMPARATIVE ANATOMY 



CHAP. 



Sub-Order 2. Tellinacese. 

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

 TelUnid^ (Tellina). Fam. Donaoid* {Donax), Mactridse (Afactra). 



Sub-Order 3. Veneracea. 

 Dimyarian with somewhat folded branchial lamellfe. Siphons separate, and foot 

 large. Fam. Veneridffi [reinis, Merrtrix [Cijth:iva\ Tapes). Fam. Petricolidae: 

 boring muscles. 



Sub-Order 4. Cardiacea. 

 Dimyarian or Monomyarian. Branchial lamellse much folded. Mantle closed 

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



710, 



Fig. 26.— Anatomy of Gardium tuberculatum, left aspect (after Grobben, Leuckart, and 

 Nitsclie, Zool. JVandtofelii)- v, Foot ; go, gonad ; S, shell ; Pa, mantle ; os, labial palps ; o, mouth; 

 Ml, anterior adductor muscle ; (s, oesophagus ; m, stomach ; I, digestive gland ; d, intestinal 

 canal ; g02, genital aperture ; noi, pericardial aperture of the kidney ; V, ventricle ; At, auricle ; 2^, 

 pericardium ; no, aperture of the kidney in the mantle cavity ; n, kidney ; Jfg, posterior adductor ; 

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

 of the mantle cavityj with anal siphon As ; Bk, branchial chamber of the same cavity "with 

 branchial siphon Bs ; Br, ctenidium. 



(Ccw'rfmm [Fig. 26].) Fam. Chamidse : Dimyarian. Valves of shell unequal. (Chama, 

 Diceras, Requienia.) To these the fossil forms Mmiopleuridce, Caprinidce, Sip- 

 puritidce,''EadioUtidtc. Fam. Tridacnidse : Monomyarian. [Tridacna, Hippopus.) 



Sub-Order 5. Myacea. 

 Dimyarian with folded branchial lamellse. Tendency towards concrescence of the 

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

 pedal cleft of the mantle still very large {Psamonobia). Fam. Hesodesmatidse, 



