174 BULLETIN OF THE 



fourth the circumference of the body, lies midway between anterior and pos- 

 terior border. Five similar lateral lines of black pigment alternating with 

 those of the dorsal region are found on the sides of the larva. These markincs 

 are placed in two lines, and are found on each segment, but do not join the 

 dorsal series of markings, since they are placed in different regions of the body 

 segments, which are not continuous. On the ventral side of the larva, similar 

 lines of black pigment also appear ; but, instead of extending across the medial 

 hne, as the markings on the back, they are arranged in two series of parallel 

 markings, of which there is a row on either side of the median line. 



The number of segments in the next oldest larva has increased to seven, or, 

 if we include the terminal, to eight. The pattern of color in each segment is 

 the same as that in the younger larva abeady described. In this, the number 

 of pigment spots on the head has also increased. At the base of the cephalic 

 appendages, near their origin under the ciliated ridge, more especially in the 

 ear-like protuberances (" auricles ") which carry the embryonic setae, there 

 will also be noticed prominent patches of crimson pigment. 



Spines indicating the position of future parapodia have appeared in the body 

 segments, although the lateral protuberances are still quite small. The spines 

 of the penultimate segments in many specimens are much longer than the 

 others. The intestinal tract, with the exception of the bend which the oesoph- 

 agus makes just before it opens into the stomach, follows an almost direct 

 course from the mouth to the vent. The lips and walls of the oesophagus are 

 richly ciliated. The external walls of the body are sparsely covered with 

 small black pigment dots. 



Aricidea sp. ('). 



Plates II. and VI. 



A series of larval Annelides referred to the genus Sjno has been described by 

 Claparede and Metschnikoff.* The youngest larva, which is here considered 

 the young of Aricidca,-f closely resembles the oldest which they describe. 



The youngest larva of this genus has a close likeness to the young Spio (p. 

 173), but differs from it in having three pairs of setae, one upon the head, a 

 second on the body at about two thirds the distance from the mouth to the 

 posterior end of the body, and a third at or near the posterior terminal segment. 

 In very young larvoe these spines are very short. The head is more rounded 

 than that of Sjno, but like it has two ear-like lappets from which the tempo- 

 rary bristles below the ring of cilia arise. There are no eye-spots, and instead 

 of well-bounded ocelli irregular patches of pigment are found on the dorsal 

 surface of the head in a position where eye-spots are later to be seen. 



The temporary head bristles are smooth, and destitute of the lateral spurs 



* Zeit. Wiss. Zool., XIX., 18G9. 



t Aricidea "Webster is not found in our waters. It was taken by H. E. Webster 

 on the Virginian coast. Trans. Albany Inst., Vol. IX., 1870. 



