ANDREWS: ANNULUS yENTRALIS, 
461 
On these assumptions a right-handed C. virilis would be funda¬ 
mentally like a left-handed C. affinis and in both species these seem 
to be the rarer forms. 
Structure in Cambarus clarkii .— Some thirty-one females of C. 
clarkii from New Orleans when studied in November had only small 
eggs in the ovaries and no sperm in the annuli. In the males the testes 
were small but the vasa deferentia contained apparently mature sperm. 
No pairing habits were seen, but one female kept with males laid eggs 
in March and these developed and hatched. 
The annulus in this species has the usual position but it is markedly 
small and inconspicuous in comparison with the annuli of the above 
two species. The median transverse ridge upon the fifth thoracic 
sternum is also small. The annulus is movable dorsally upon its 
anterior hinge and by moving the fifth legs one may push the fifth 
sternal ridge against the posterior face of the annulus which enables 
one to suppose the annulus may be discharged by pressure as was 
thought to be the case in C . affinis. 
The annulus is whitish or light red and may have a blue area right 
and left upon its anterior face; it is thus noticeably paler than the 
adjacent parts which have the vivid red color of the under side of this 
highly colored species. 
The form of the annulus (pi. 47, fig. 34) is that of a truncated hill 
very slightly dished on top so it seems to depart markedly from the 
preceding forms in having no central depressed area. It is also char¬ 
acteristically smooth, simple, and free from protuberances, while its 
plain single suture is all in sight. The central plateau is bounded by a 
steep slope leading down gradually to the general level of the adjacent 
sternal surface so that the exact delimitations of the transversely and 
sharply ellipitical annulus are not at all well marked. The posterior 
view (pi. 48, fig. 37) well shows the truncated character and the 
slightly greater elevation of the median posterior border. The anterior 
face (pi. 48, fig. 38) shows a deep median groove from which the 
sinuous suture passes back. 
The suture passes from the median line to the right or the left, in 
one angular semicircle and returns, anteriorly, nearly to the median 
line to break through the anterior border of the plateau into the wide 
median groove on the anterior face of the annulus. This anterior 
groove seems an exaggerated representative of the corresponding part 
of C. affinis (pi. 43, fig. 1). 
