128 E. A. ANDREWS. 



end was crossed by a sharp fold and the cut de sac was more pro- 

 nounced. In some the posterior face of the annulus, which pro- 

 jected and overhung considerably, bore a curved transverse ridge 

 strongly suggesting the posterior rim of the adult annulus, Fig. I. 

 In a large female of 13 mm. the groove was as in Fig. 1 1, though 

 a little longer. 



The single layer of epidermal cells under the shell was still 

 visible as a series of polygons as in the third stage. While the 

 annulus itself showed no setae upon it in any stage the transverse 

 ridge of the sternum behind it bore scattered over it some four 

 or five sharp seta in the third stage, about ten in the fourth and 

 twenty in the fifth. 



The fifth stage includes individuals 15-18 mm. long, and in 

 them marked changes had taken place in the annulus, but before 

 describing these we will refer to a few observations made upon the 

 developing annulus in an early stage of another species, C. 

 Clarkii, from New Orleans. Here also the young reared in the 

 laboratory had no annulus in the first and second stages, which 

 were about five and six millimeters long, and they also showed 

 no external sexual differences. Young of this species were seen 

 by Hagen. 1 when .3 inch long and still on the abdomen of the 

 female ; in which the females had no pleopods upon the first ab- 

 dominal somite, but showed the openings of the oviducts, while 

 the males had the first pleopods as little knobs longer than 

 broad and turning inward. Later Faxon - stated that the young 

 of this species from under the abdomen of the parent had the 

 general form of the adult when 7 mm. long. Evidently both 

 authors saw the third stage only. 



Eggs hatched April 21 reached the third stage June I, but no 

 observations were made upon the annulus till they had passed 

 into a later stage, June 19, and were 1 1 mm. long. In this condi- 

 tion the male and female were much like specimens of C. affinis 

 of that length, but the first pleopods in the female were much 

 smaller and in the male noticeably shorter than in C. affinis. 



The groove on the annulus of the female now formed a deep, 

 closed in cavity, Fig. 12, which is enlarged to the same extent as 



1 "Monograph N. A. Astacidte," Harvard, 1870. 



2 " Revision of the Astacidje," Harvard, 1885. 



