ORDER III 



TELKODKSMAC'EA 



423 



Family 44. G-astrochaenidae. (I ray. 



Shell substance as in ,sW/mo : valve* .7/1, /, /!;/.// guying /'// _/'/-..// : ,nl<lu,-tnr scars 



the anterior smaller : jmlfinl >/'//> </'//. ///"/<////.- >-//;,y// : <//' ////< ; /- 

 res-ilium external, paririncular ; hi mi, /<//// ^ .<//)//// <,/,>/,/, -,///////// / 



,,1, llhllnllti ; ilililllill frrif Ilintlil f 



.1,1 external protective th<> to supplement 

 its burrow, but to which it is in no icay 



( IVmiian. Trias to 



Fie. 7M!. 



Jl.-sli. 



Eocene (Sables" inoyens) ; 

 Valniandois, near Paris. 



]><:<li>n<l- 



Middle 



Jura; Balin, near Cracow. 

 Cast of burrow including 

 one of the valves, i/j. 



This ^roiiji stands hetween tin- Mn<",,i 

 and A</'Xinacea, verging >n tin- latter. 

 Many of its characters are adaptive, and are 



repeat rd ill the h'/ixiji/<f>i><i<-<'i>, hut morpho- 

 logically its relations to the 



,-eein 



Gastrochcu rux,Spengler (C'A'" /*". l!.-t/. ; 

 Rocellaria, Blaiuv.), (Figs. 782, 783). 

 Bores cylindrical or pear-shaped cavities in rock, shell, or coral. Trias to .Knvni. 



Fistulana, Brug. Secretes calcareous tubes which stand upright in the sand or mud. 



Superfamily 17. ADESMACEA. Blainville. 



Gills with direct and reflected laminae, lony, united^ extended into the 

 siphon ; posterior adductor usually in front of the visceral ganglion, anterior adductor 

 external to the cavity of the valves, exerted in a contrary sense to the posterior muscle ; 

 hinge margin reflected, edentulous; ligament obsolete; a myophoric process extending 

 freely into the valve from the sub-umbonal car if if. 



Family 45. Pholadidae. Fischer. 



Shell cellido-crystaUiiK, tritli tit in epidermis; valves more or less goring in front 

 and behind, with inconspicuous beaks and reticulate, often spin<> * -nljitnre; in tlw 

 adult supplemented by accessor// slu-Uij pieces, always- attached to the valves, but not by 

 nn t.rtt'rior shelly tube like tlxtf of th# Gastrochaenidae ; the antero-dorsal margins more 

 or less extensively reflected, the postrro-rentral approximated; pallial line sinuated, area 

 none ; ligament and rcsilium usually absent, an obsolete remnant of the resilium and 

 chondrophore sometimes present in the left valve. I Carboniferous, Jura to Recent. 



Pholas, Linn. (Fig. 784). Surla< > divided by grooves into areas which often have 

 diverse sculptuiv ; the adult often provided with accessory -lirlly plates, each of which 



<; TS.J. 



I-IKJH* l.,r<:*infi, Watelfit. Eoct-nc ; Cnisr <!.- la Motlir. 



when seated in front of the beaks has been named a " protoplax," when above the 

 beaks, "mesoplax," when behind the beaks between the valves " metaplax," and when 

 between the valves ventrally (Martesia), " hypoplax." A calcareous septum, secret id 

 after the completion of the burrow, and occupying the pedal gape of the valves, is 

 called the " callum." The addition of these plates and appendages during growth so 



