Key to Plate V — Continued 



The oldest stage raised by Brooks. Compare PI. I, fig. 12. 



Fig. 27. Much older larva (umbo-stage) from the left side, swimming. 

 Not e(j[ually magnified with preceding. (Compare PI. I, fig. 16). 



Fig. 28. Similar larva with velum flattened against slide, viewed 

 from ])ehind. 



Fig. 29. Similar larva, viewed from the front. 



Fig. 30. Full-grown larva (compare PI. I, fig. 20), from left side; 

 anterior end tilted up, valves of shell opening for protrusion of velum (v) 

 and foot (/). Through the left valve can be seen the gill [g), pigment-spot 

 (e), liver (Z), intestine {%), anterior and posterior adductor muscles {ad pd), 

 and edge of mantle (mn) . 



Fig. 31. Full-grown larva, from left side: ad, pd, anterior and pos- 

 terior adductor muscles; v, velum; /, foot; g, gill (left inner hemibranch); 

 mn, numtle; m, oe, mouth, oesophagus; st, stomach; I, liver; i, intestine; 

 a, anus; um, umbo. 



Fig. 32. Full-grown larva from right side — the position in which it 

 becomes attached, ad, anterior adductor; pd, posterior adductor; rv, 

 right valve; b, left valve; i, intestine; e, pigment spot; Z, liver; v, velum; 

 /, foot; 17171, edge of mantle; g, gill (right inner hemibranch); ot, otocyst. 



Fig. 33. Spat of 1 mm. length (compare PI. II, fig. 5) Iv, left valve 

 of the larval shell; rv, right valve of the larval shell; ss, spat shell; mn, 

 mantle; m, mouth; st, stomach; vg, visceral ganglion; pd, posterior 

 adductor muscle; rig, right inner hemibranch (same as g of fig. 32); lig, 

 left inner hemibranch (same asg of fig. 31); a, anus; i, intestine. 



Fig. 34. Spat of 2 mm. length (compare PL II, fig. 7); fo, larval shell: 

 .ss, spat shell; p, palps; rig, right inner hemibranch; lig, left inner hemi- 

 branch; -y^, visceral ganglion; mn, mantle: pd, posterior adductor muscle; 

 ml, line along which the muscle travelled in the growing spat; I, liver. 



