450 PROCEE'DINiGS OF THE NATIONAL MUSEUM vol. 91 



Width of the orbital and extraorbital sinuses, where referred to, 

 has been measured in line with the tips of the orbital spines, from 

 the extremity of the spine to the rostral margin, and from the spine to 

 the inner margin or slope of the anterolateral spine. The orbital 

 spine (or spinule) is the actual spine or spinule marking the outer 

 or distal end of the orbital margin, without reference to scabrosities, 

 denticles, scales, or tiny, often microscopic, spinules that may arm or 

 persist on the orbital margin of some species. In most species the 

 outermost of such a series of orbital scabrosities becomes so developed 

 as unmistakably to become the orbital spine or spinule. 



The length of the anterolateral spines in relation to the eyestalks 

 is perhaps not a very reliable character, owing possibly to differences 

 in contraction as a result of preservation, yet in a species like A. 

 sanloremo the anterolateral spines exceed the eyestalks, while in 

 A. ahtao and A. riolimayana^ for example, they generally fall short 

 of the posterior margin of the cornea. 



I have not been able so far to "pin down" the relative proportions 

 of the areolations of the carapace in a way to permit their satis- 

 factory use in specific description. The areola itself is rather elongate 

 in some species, very squat in a number of others, and quite different 

 in the relation of its posterior lateral margins to the lateral furrows 

 or suture lines of the cardiac area, in at least two nearly related 

 species, A. ahtao and A. rioUmayana. 



Most of the species of Aegla exhibit a tendency toward smoothness 

 and bluntness, even to the suppressing of spines in the older, more 

 developed specimens. In A. parana quite the reverse is true; there 

 seems to be an accentuation of the spininess of this species, the fully 

 developed adults are very spiny or at least more prickly appearing 

 than any other one of 20 species or subspecies described. 



Aegla parana is the only Aegla having the ambulatory legs strongly 

 spined above and, with A. sanloremo and perhaps also A. prado^ the 

 only species having reasonably strong spines below near the anterior 

 end of the ambulatory merus. Only one ambulatory leg, the first 

 on the left side, has been figured for each of the species dealt with 

 in this paper, chiefly to show the proportions not as yet clearly 

 proved to be of specific value. 



In the majority of the Aeglas the sternal plate between the chelipeds 

 carries no particular armature ; in a few species a very definite, often 

 corneous-tipped tubercle or low conical spine is to be found on the 

 median line toward its anterior end; the anterolateral angles of this 

 particular plate are sometimes markedly produced or even spiniform. 



Except for the contours of the epimera of the second (in lateral 

 view, apparent first) abdominal somite no particularly noticeable 

 specific differences have been observed in the abdomen or the tail 



