272 ^S', I. Smith — Arnphipodus genera, 



projjodus is about as long ami nearly as wide as the body of the 

 merus, is articulated close to the base of the carpus, and armed with 

 a single minute seta on each edge near the distal end. The dactylus 

 is very short and stout, with the solid chitinous tip turned sharply 

 backward and upward in an acute hook and armed with a sharp 

 tooth on the outside at the point of curvature. The fourth and fifth 

 perseopods are slender and of nearly the same form as in Ericthonius 

 difforniis. The foui'th are about once and a half as long as the third, 

 the basis is much broader than the other segments and about a fourth 

 longer than broad ; the ischium is small and nearly square ; the 

 merus is twice as long as the ischium and very slightly broader ; the 

 carpus is not quite as long as the merus but of about the same width ; 

 the propodus is about as long as the merus but much narrower ; the 

 dactylus is stout and hooked very much as in the third pair ; the 

 distal angles of the merus and carpus are armed with long setai 

 which are longest and most numerous on the posterior distal angle of 

 the carpus, which projects in a small lobe. The fifth pair are a little 

 longer and proportionately a little more slender than the fourth pair, 

 but do not diifer in other respects. 



There are, apparently, only three pairs of branchial lamelke, a sin- 

 gle lamella being borne upon each coxa of the first, second and third 

 pairs of peraeopods. 



Of ovigerous lamellaB there are also only three pairs and these are 

 borne upon the cox^e of the second pair of gnathopods and of the 

 first and second peraeopods. 



The first segment of the pleon is slightly shorter than the seventh 

 segment of the pera^on, and the second and third are successively still 

 shorter. The three pairs of pleopods (Plate Ila, figure 5, a, b, c), in 

 marked contrast to those of most Amphipoda, difier remarkably 

 among themselves in the relative proportions of the outer and inner 

 lamellae, and diminish greatly in size from before backward. This is 

 undoubtedly an adaptation to the position of the animal in its closely 

 fitting tube, with the posterior segments of the pleon bent closely be- 

 neath the anterior segments, leaving very little room for the action 

 of the pleopods. In the first pair of pleopods (figure 5, a) the base 

 is about as long as the base of the first uropod and more than half 

 as broad as long ; the inner lamella is a half longer than the base, 

 narrow, and both margins are furnished with long, plumose setae ; the 

 outer lamella is very little shorter than the inner, narrow distally, 

 but broadly expanding proxinially till the breadth is equal to half 

 the length, and then suddenly narrowing to the base ; the distal two- 



