448 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 91 



which are arranged more or less transversely in the distal half of 

 the ridge and somewhat or at times almost wholly longitudinally at 

 the proximal end of the ridge. In some species the nodulations be- 

 come tuberculiform, and in still others, such as A. denticulata and 

 A. castro^ actually replaced by sharp-pointed conical spines. 



On the middorsal line of the carpus in a number of species there 

 is a suggestion of a second though much less well formed ridge in 

 the shape of an irregular, more or less scattered, longitudinal row 

 of scabrosities somewhat larger than the others that may roughen 

 the surface of the carpus; in A. parana there is a middorsal row of 

 small sharp spines, few in number. 



The upper longitudinal margin of the merus of the cheliped may 

 be very sharply and conspicuously spined, or else tuberculated with 

 apices of tubercles scabrous, or virtually unarmed as in A. jujuyaina 

 and A. hv/mahuaca. 



The anterior margin of the merus may be perfectly smooth and 

 evenly rounded oil (JL. hutnahuaca) ^ actually spined, or more or less 

 finely denticulate; in other species it will have middorsally a more 

 or less definite swelling, nodule, lobe, or even tubercle {A. odebrechtii) 

 which may anteriorly be minutely spinulated whether the rest of the 

 anterior margin is similarly armed in part or not. As with many 

 of the other morphologic features of Aegla^ there seems to be con- 

 siderable variation in the degree of development exhibited by this 

 lobe, so that its specific importance, in the light of our limited 

 knowledge of the members of the genus, cannot be satisfactorily 

 determined. 



The basis and ischium of the chelipeds are fused to form one joint. 

 Below, toward its proximal end, there are three transverse, more or 

 less impressed lines. The anterior and posterior lines mark muscle 

 attachments ; the middle one constitutes " 'a fracture plane' at which 

 separation of the limb takes place in [this and] many [other Crus- 

 tacea] Reptantia" (Caiman, 1909, p. 273). In describing the arma- 

 ture of the "inner margin of the ventral surface of the ischium" 

 only that portion of the ischium proper, or of the fused joint, basis- 

 ischium, beyond or distal to the anterior of these three lines of 

 demarcation is referred to. 



There seem to be two principal types of rostra to which the various 

 species of Aegla may be referred. The first of these I shall call the 

 ridge-roofed (Atlantic) type. In this the dorsal surface rises from 



^ A. intermedia, described by Girard (1855, p. 255) but not lyet rediscovered, is described 

 as having two rows of spines on the carpus, its only recognizable or rather distinctive 

 character that it shares with A. denticulata and A. castro. The second of these certainly 

 does not occur in Chile and so could not be confused with Girard's species, from which 

 A. denticulata is at once set off by the longitudinal keeling of its carapace and the con- 

 spicuous saw-teeth arming the lateral margin of the posterior portion of the carapace. 



