354 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



The fifth abdominal somite is somewhat louger thau those in front of it, aud about twice as 

 long as the sixth. The telson sometimes presents slight variations, but most of its characteristics 

 are well marked, so that there is usually no difficulty in distinguishing the species by examining it. 

 It is considerably wider than long, and its median portion is occupied by a rounded prominence, 

 which consists of three broad, convex rounded cariiue, none of them ending in spines ; the median one 

 is louger than the others aud spatulate at its posterior end, while the others have both ends obtusely 

 rounded aud alike ; external to the proximal end of each lateral carina, and almost directly under the 

 tip of the second, or intermediate dorsal carina of the sixth abdominal somite there is a small polished 

 hemispherical tubercle. The edge of the telsou is folded into six teeth, of which the sub-medians 

 are largest aud project farthest backwards; the tips of the intermediates are distinct and reach 

 about halfway to the tips of the submedians; the laterals are obsolete on the dorsal surface, al- 

 though thin, small tips are distiuctly visible on the flat ventral surface of the telson ; each of these 

 six teeth carries a dorsal carina ; that of the lateral is marginal and nearly linear, while the otliers 

 lie in the dorsal axes of the teeth and are thick and convex; that which lies above the subuiedian 

 tooth is short, and lies in the same longitudinal plane as the external cariua of the median promi- 

 nence of the telson, while that which lies above the intermediate tooth runs nearly to the anterior 

 edge of the telson; the median edges of the submedian teeth are minutely serrated, slightly con- 

 cave, and meeting at an acute angle. There is a minute, nearly obsolete, tooth in the angle be- 

 tween the submedian and the intermediate, aud the tips of the submedians are occasionally, but 

 exceptionally, tipped by movable acute spines. The dorsal surface of the basal joint of the uropod 

 ends posteriorly in an acute spine with a small lobe on the outer side of the base: its ventral sur- 

 face ends posteriorly in a curved process divided into two acute curved spines, of which the outer 

 is much the stouter and usually considerably louger than the inner, although they are occasionally 

 nearly equal ; the outer one has no marginal tooth. The paddle of the exopodite is about halt' as 

 long as the second joint, which carries a central terminal immovable spine, and usually eleven 

 rarely twelve, aud still more rarely ten movable spines, of which nine are marginal aud the tenth 

 and eleventh terminal, largest, and central to the paddle. The eyes are cylindrical, with rounded 

 cornea}; and the first and second antennae are about equal in length, and more than half of t!>e 

 second joint of the shaft of the first antenna is exposed in front of the eye. 



In the Bahama Islands this species presents two well-marked color variations, which occur 

 side by side, specimens of both sorts being often found in burrows less than au inch apart. In the 

 one form the color is a uniform dull-olive without spots or markings of any sort, as shown in PI. in; 

 while the other form, which is copied iu PI. 1, Fig. 2, is more transparent aud is delicately mottled 

 over the entire dorsal surface iu au iutricate but constant pattern of greyish-green pigment so 

 distributed as to form three transverse bands across the carapace and the large joints of the 

 raptorial claws and line transverse bands across the telson, while over the rest of the dorsal 

 surface it forms a complicated reticulum. This difference is not sexual, for I found both males 

 and females of each color; nor is it distinctive of age, for, while all the largest specimens were of 

 the uniform green color, I found specimens of each color of all sizes except the largest. It is not 

 probable that there are two constant color varieties living side by side in the Bahama Islands, 

 and 1 am disposed to think that the mottled transparent specimens are those which have recently 

 moulted, aud that the color becomes more uniform as the cuticle hardens. 



Iu the Bahama Islands this species inhabits burrows which it constructs iu the coral rock or 

 in masses of coral in shallow water, ami, as nearly all the localities where its presence has been 

 recorded are in the coral area, it is probable that this habit is pretty generally retained by the 

 species all over its habitat. I have found it most abundant in lagoons and sounds on shelving- 

 beaches which are bare or nearly bare at low tide; and when a beach of this description is over 

 hung by a limestone cliff, from which fragments fall into the water, each fragment is honeycombed 

 by their burrows. A crack or natural depression in the rock seems to be selected by the animal 

 when about to construct a new burrow, for most of the burrows opened into such cracks. The 

 mouth of the burrow is nearly circular and only a little larger thau the body of its inhabitant, but 

 just within it widens out into a flask-shaped cave (PI. in), with smooth, even walls aud regular 

 curvature, aud large enough for the auimal to coil up or turn around inside it. Most of the burrows 

 are horizontal, but many are vertical with the opening below, and a few are vertical with the 

 opening above. 



