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. 

 No1 equally magnified with preceding. (Compare PI. I, fig. 16). 



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

 from behind. 



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



Fig. 30. Full-grown larva (compare PL 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 (y), pigment-spot 

 (e), liver (I), intestine (i), anterior and posterior adductor muscles (ad pel), 

 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, mantle; m, oe, mouth, cesophagus; 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; Iv, left valve; i, intestine; e, pigment spot; I, liver; v, velum; 

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



Fig. 33. Spat of 1 mm. length (compare PL 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 asgr of fig. 31); a, anus; i, intestine. 



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

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

 branch; vg, visceral ganglion; mn, mantle; pd, posterior adductor muscle; 

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



