MARINE CRUSTACEANS. 7 1 1 



9. Sphaeroma [Exosphaeroma ?] globicauda, Dana. 



Spheroma globicauda, 1853, Dana, U.S. Expl. Exp., \o\. xni. p. 781, pi. 52, fig. 9 «, h. 



Dana gives the following description : — ' Body nearly smooth, in part very fine granulous 

 and pubescent. Abdomen subtriangular, very tumid, excepting the parts towards the margin 

 around ; at extremity a deep fissure, which at its inner end is produced a short distance 

 transversely in either direction. Caudal ajipendages reaching slightly beyond line of abdomen ; 

 inner lamella the broader and slightly the longer, broadly rounded at apex ; outer having the 

 outer margin much reflexed.' Then, after stating that the habitat was ' Nassau Bay, Fuegia,' he 

 adds : — ' Length of body, two and a half lines. The fissure in the extremity of the abdomen 

 is of peculiar depth and shape ; the part of the surface of the abdomen anterior to its inner 

 extremity is a little raised, independently of the general globose elevation which characterizes 

 the whole segment anterior to this raised point. The minute hairs of the surface and slight 

 granulation are seen with a lens most distinctly on the caudal segment.' 



Specimens from the lagoon at Minikoi agree so well with this account that nothing but 

 the difference of size, which in them scarcely exceeds 3 mm., could cause any doubt as to 

 the identity of the species. An examination, however, of what may confidently be regarded 

 as the sexes of one and the same species leads to the conclusion that the aperture in the 

 telsonic segment belongs only to the male. It is probably a character of the adult, since all 

 the smaller specimens as well as the female carrying young are devoid of this transversely 

 rounded opening. Oymodoce cordiforaminalis, Chilton, has the aperture of a rather different 

 shape, but is otherwise a species so similar to the present that it will be interesting to 

 learn whether it exhibits the same sexual difference. 



The head has a blunt rostral point between two emarginations. In the male the seventh 

 segment of the peraeon is slightly indented at the middle of the hind margin, which is 

 smoothly convex in the female. The pleon has a very short first segment overlapped by the 

 peraeon. This segment is closely united to a composite segment, probably representing the 

 second to the fifth, the angles of the fourth and fifth being to a certain extent distinct but 

 strongly overlapped by those of the preceding segment. 



The eyes are not very large, but prominent, conspicuously faceted. The first antennae 

 have a stout composite basal joint, followed by a third joint not much longer than broad, and 

 much shorter than the first joint of the eight-jointed flagellum, which exceeds the peduncle 

 in length and has sensory filaments on the terminal joints. What is here regarded as the 

 first joint of the flagellum coiTesponds with the third joint of the peduncle in Chilton's de- 

 scription. 



The second antennae are rather longer than the first, the second joint longer than the 

 first or third, the fourth than the second, the fifth than the fourth, but not ' nearly twice 

 as long' as in Chilton's species. The flagellum is nine-jointed. 



The mandibles have a strong molar and tridentate cutting edge with accessory plate and 

 spine-row, and three-jointed palp. The inner plate of the first maxillae is tipped with four 

 setae. But none of the mouth-organs appear to off^er any very distinctive features except the 

 maxillipeds. These differ in a marked degi-ee from those of Sphaeroma serratum, as also 

 from those of Sphaeroma rugicaiida. Leach, but neither do they fully agree with those that 

 have been described in any of the species of Exosphaeronia or Cymodoce. The fourth joint is 

 considerably longer than the fifth, and each of these is distally expanded on the inner side. 



