REPORT ON THE CRUSTACEA MACRURA. 539 



pleon is nearly three times as long as the carapace and terminates in a tclson that is 

 rounded at the extremity and fringed with ciliated hairs, flanked with a small spine on 

 each side, and one on each side of the median line. 



The ophthalmopod is orbicular and projects free in front of the frontal margin. 



The first pair of antennae carries two short flagella. The second pair is styliform and 

 supports a small bud-like process near the middle. 



The mandibles and first pair of siagnopoda have not been examined. 



The second and third pairs consist of a peduncle and two unequal branches, the 

 longer, which I take to be the basecphysis, is tipped with four or five long cfliated hairs ; 

 the shorter, which appears to be the incipient condition of the permanent joints, terminates 

 in three or four simple hairs. 



The first and second ' pairs of gnathopoda resemble the preceding two pairs of 

 appendages but are slightly longer. 



The first pair of pereiopoda is in an advanced condition and chelate, but unequal in 

 form and proportion ; that on the right side is the smaller, carries a multiarticulate 

 basecphysis, and consists of a united ischial and meral joint, a short carpos, a propodos 

 that has the margins parallel and forming with the dactylos a well-developed chela ; that 

 upon the left side differs in having the propodos very much larger, and the margins of 

 that joint are not parallel, but much larger at the carpal extremity, gradually narrowing 

 distally and terminating in a sharply pointed chela. The three succeeding pairs are 

 biramose and resemble the four anterior, excepting that they are rather longer. 



Each of the anterior five somites of the pleon carries a pair of short biramose pleopoda ; 

 the sixth is associated with the telson and has as yet no appendage. 



The Megalopa was got from the ovum of a near ally of Alpheus minus, but 

 differing in having a long powerful tooth on the outer margin of the scaphocerite, the 

 foliaceous part being smaller, membranous and very thin. I previously (he. cit., supra) 

 named this specimen Homar alpheus, making it a separate genus, from the impression 

 that species producing a Megalopa could not be placed in the same genus as those 

 producing a Zoea. 



Geographical Distribution. — The several species given in the following list, with 

 their habitats and depths, so far as known, appear to belong to the shallow waters 

 or to depths less than 60 fathoms. Only one locality is recorded with a greater 

 depth than this — Alpheus avarus having been procured off Japan, at Station 234, in 

 2675 fathoms, but as this species is known to inhabit comparatively shallow seas, this 

 case is probably due to some acccidental circumstance. Their geographical range is 

 very extensive between the north and south temperate zones, and in one instance a 

 specimen of Alpheus minus has been recorded from an inland fresh -water pond in south- 

 west Colorado. 



