674 PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. XXXI. 



are compelled to fall back upon his figure, which is a fairl}^ good one, 

 for our information. That the three pairs are all uniramose, is 

 extremely improbable, and Olsson's description must be received as 

 much the more accurate. 



This latter author ssljs, in speaking of the smallest chalimus found 

 (0.8 mm. long), that it possessed two pairs of swimming legs, .each 

 with a single basal joint, and two one-jointed rami. 



A little larger specimen (1.2 mm. long) showed vestiges of the third 

 legs, while a larva two millimeters long had all the "abdominal feet," 

 but the rami, except those of the first pair, were not jointed." This 

 corresponds with the condition in the Caliginee and Euryphorinaj and 

 hence is what would naturally be expected for the present genus. 



The fourth segment is still fused with the genital segment, and the 

 two bear no appendages. The abdomen consists of a single short and 

 wide joint bearing the small and elongate anal lamina. These last 

 two joints also diminish regularh" in size from the third thorax joint, 

 so that the whole'posterior body of the chalimus tapers evenl}- toward 

 the abdomen. 



The second antennae are noticeably elongated and slender; the two 

 joints are about the same size, while the terminal claw is short and 

 abruptly .bent over toward the second joint into the form of a sharp 

 hook. Nothing is said of the other appendages save that the mouth- 

 parts have the same general shape and arrangement as in the adult. 

 In fact they furnish in this one of the best evidences of the identity of 

 the larva. 



In this young chalimus, for such it is proved to be by the stump of 

 a frontal filament still attached to the frontal plates, the transverse 

 groove between the head and first thorax segment is perfectly straight, 

 while that between the first and second thorax segments is slighth^ 

 curved forward at the center. 



This forward curve is increased in later development, so that on a 

 larva 2.5 mm. long it projects quite a little way into the posterior 

 portion of the carapace (fig. 2). 



This larva and the one following, the next two stages known, Avere 

 found b}^ the author among some adults of Trehius exilis^ a new species 

 obtained by Prof. W. A. Herdman from Rhlnopte^'a javanica at Ce}"- 

 lon. The lateral processes on the sides of the second segment in this 

 larva are nearly as large as the posterior lobes of the carapace. The 

 third segment is considerably narrower than the second, but is still 

 wider than it is long. The fourth and genital segments have been 

 separated; the former has been elongated until it is now longer than 

 wide and is of a broad spindle shape, widest at the center. 



The genital segment has a curious shape; each of the posterior 

 angles projects strongly sidewise, is well rounded, and armed with two 



«01sson, Prodromus faunre Copepodorum parasitantium Scandinaviee, 1869, p. 15. 



