164 CANON A. M. NOEMAN ON A CEUSTACEAN 



of very much stouter proportions than those of the first feet ; the first joint carries one 

 distal external seta and the inner margins of both joints are densely setose, the inner 

 branch has three joints nearly subequal to each other in length and are densely setose 

 on the inner margins and the apes, the outer two-jointed branch has the first joint equal 

 in length to the first two joints of the inner branch ; the second joint is fully twice as 

 long as the terminal joint of the inner and is setose both on the inner and outer 

 margins ; the third, fourth, and fifth feet are of very similar structure to the second 

 just described. The sixth pair (PI. 35. fig. 3) has the first joint of the peduncle long 

 and comparatively narrow ; there are no conspicuous setae either on that or the following 

 joint. Both rami are two-jointed and furnished with long setae, especially on their 

 inner margins. 



The last joint of the metasome (PI. 35. fig. 7) carries two spines, which are considerably 

 longer than the breadth of the segment from which they spring ; these spines have the 

 margins serrated. Besides these spines the body terminates in two one-jointed uropods 

 (PI. 33. fig. 6) ; these uropoiis are more than twice as long as the preceding segment, on 

 the outer margins they carry two plumose seta? and two terminal, while their inner 

 margins are densely clothed with similar setae ; the outer margins of these rami are 

 dentate from the base to the origin of the first external seta. With respect to the 

 organs of generation, I am not able to describe them satisfactorily, and it was chiefly 

 witli a view of examining them more fully that I desired to procure fresh specimens of 

 Synayoga. Posteriorly to the sixth pair of feet on the first segment of the metasome a 

 peculiar organ is found which appears to be that of the male. At half its distance 

 from the base a portion bends downwards and terminates in a conical point which 

 appears to be the penis ; beyond this point the limb arches and is gradually attenuated. 

 PI. 35. fig. 4 represents this appendage as seen from side. Pig. 5 (which is, however, 

 partly diagrammatic) gives the appearance as seen from below. We find other specimens 

 in which the first segment of the metasome is more produced downwards than the last 

 segment of the mesosome (PI. 35. fig. 6), and this produced segment is crenulated at the 

 extremity and on the front margin ; this would appear to represent the vulva of the 

 female, and thus it would seem that the two sexes are separate. 



Behind the antenna? there is an organ which occupies the place of what Lacaze-Duthiers 

 calls in Laura the first feet: the organ here can scarcely be regarded as a foot, inasmuch 

 as behind it we have six pairs of distinct feet, nor does it present the appearance of a 

 foot ; nevertheless it would seem to discharge part of the functions of the first foot in 

 Laura, inasmuch as I take the papilla to be the orifice of the oviduet which brings the 

 ova from the ovary, situated beneath the mantle. Of this organ there are given three 

 illustrations (PI. 34. figs. 8, 9, 10), but for the differences between them I am unable 

 to account. 



PI. 33. fig. 5 represents a tubule containing ova from beneath the mantle. Fig. 4 

 represents a portion of the margin of the mantle and shows the more fully developed 

 ova within. 



The several genera of the order Ascothoracica differ in development of the various 

 organs, and these changes have, doubtless, been brought about by the more or less 



