83 



are directed obliquely outwards, projecting considerably from the body; 

 it seems fairly certain that a muscle is passing between the ends of the 

 hooks. The body rods are simple, with irregular thorns along their outer 

 edge, not widened in the point, which is apparently not specially adapted 

 to the attachment of an abductor muscle. The postoral rods are in the 

 main as in species a; only the left being slightly abnormal in its basal 

 part. Both these rods are broken so that their length cannot be ascertained. 

 The anterolateral rods are well developed, sUghtly thorny. The recurrent 

 rods are somewhat irregular; the right one bifurcates, one branch going 

 medially, the other backwards, reaching the end of the body rod; the 

 left ends with a widening in which a rather large hole. A somewhat long 

 thorn proceeds from the base of the postoral rods, just outside the point 

 of issue of the anterolateral rod. Posterodorsal rods, dorsal arch and 

 posterior transverse rod are not yet developed. 



Species c. (PL XIII. Fig. 1). One beautifully preserved specimen of 

 this larva was found in a plankton sample from Christiansted, St. Cruz, 

 West Indies, taken on the 16. VI. 1915 by Mr. H. Faye. 



Irf its main features it agrees with species a, but the postoral arms 

 are very much longer, no less than 12 times the body length; moreover 

 the point is broken off, so that they must be rather considerably longer. 

 The preserved part is 3 mm long. The specimen has been preserved in 

 such a state of contraction of the adductor muscle, that the arms are 

 directed almost straight upwards, which gives the specimen an aspect 

 very different from that of the other species. That this is, however, really 

 due only to muscular contraction is beyond doubt, as is evident only 

 from a comparison with the two related species, b. and d., from the Gulf 

 of Panama, of which species b has the arms in the same upright position, 

 while the other, species d, has them horizontally directed. The contraction 

 of the muscle connecting the two body rods (which is quite distinctly 

 seen in the specimen) would give the postoral rods the usual horizontal 

 position. The anterolateral arms are distinct but considerably shorter than 

 in species a, hardly more than one fourth of the body length, while in 

 the latter species they are somewhat more than body length. The preoral 

 band is well developed, though not so strongly curved as in species a. 

 The postoral band has a concavity in the middle and makes a rather 

 deep downwards bend before passing on to the postoral arms; however, 

 this configuration may probably be due only to the upward direction of 

 the postoral arms ; it seems certain that on the postoral arms being hori- 

 zontally directed the postoral band must assume the same simple shape 

 as in species a and probably also be lowered down to the level of the 



11* 



