668 



at a near approaching moult. This change in the form of the rostrum 

 is of interest in connection with a case of regeneration in one of the 

 adult females. Here the rostrum had been broken off across between 

 the anterior parts of the eyes and replaced by a piece of full size but as 

 yet movable upon the old part. This new rostrum was simple and without 

 the lateral spines of the other adults, so that the regenerated part was 

 like the rostrum of the larva and would need to be perfected at a sub- 

 sequent moult, and then the course of regeneration would run parallel 

 to that of ontogeny. Possibly some of the apparent varieties of this 

 very variable species may prove but imperfect, regenerating specimens. 



Whether these young were in the first or the second stage of larval 

 life was not easy to determine, as they showed characters of each stage. 

 Crayfishes remain upon the mother both in the first and the second 

 larval stages and differ not only in size but in the perfection of the ex- 

 ternal organs. 



The larvae of these C. montexiimae have the smooth, hairless bodies 

 of first stage crayfishes, but they are long and have the spinules on the 

 mouthparts unusually well developed. 



In the first antenna there are four joints in the endopodite and five 

 in the exopodite. The sense clubs are longer than in any other larval 

 crayfish yet studied, three stand on the ultimate segment and two on the 

 distal end of the antepenultimate segment. The ear pit is oj^en, naked 

 and full of dirt. The second antenna has 30 segments in the flagellum 

 and about 15 teeth on the scale. The mandibles have three or four 

 blunt teeth, but will have six or seven at the next moult. The exopo- 

 dites of the maxillipedes are very long. And, as above stated, the tips 

 of the chelae are very much recurved, while the rostrum is but little 

 bent, though not provided with lateral teeth till the next moult. 



The long, simjile telson bears 16 very small triangular spines, or 

 papillae, eight on each side, and these show no grouping such as to 

 suggest the glandular function observed in the first stage of other cray- 

 fish, but as the larva is about to throw off its shell the apj^arence of the 

 spines may have changed since they were first made. Inside the telson 

 the last pair of pleopods is remarkably far developed and it is obvious 

 that the larva will have a fringe of long setae, which will perhaps be 

 plumose as in C. ciarlai. 



Upon tabulating the like characters in the other larval crayfish, in 

 which they have been as yet described, namely C. afflnis, C. ciarlai., C. 

 cliogenes, and Astacus leniusculus, it appeared that these young of C. 

 montexumae were more like the first stage in some respects but more 

 like the second in others. 



The chief resemblances to the first stage are: the absence of hairs; 



