20 DE. H. J. HANSEN ON BATHYNOMUS GIGANTEUS. 



Bathynomus. I must begin witli the statement that I can con- 

 tribute only two or three small additional and a few critical 

 remarks to the beautiful and exhaustive treatment by Bouvier, 

 to which the reader is referred. 



The specimen seen by me is an immature female, measuring 

 193 mm. in length, with five pairs of rudimentary marsupial 

 lamellae, the longest of which, the fourth, measures only 7*5 mm. 

 in length and 4-5 mm. in breadth. A comparison with the 

 figures in Bouvier's work shows that it belongs to B. giganteus, 

 and does not even present any deviating feature in the " epimera," 

 the abdomen, &c., worth mentioning. 



Dorsal Organ on tlie Head. — In the figure on pi. 1 in 

 the French work, showing the animal from above, is seen a 

 whitish spot in the central line of the head at a short distance 

 from its posterior margin. A closer examination shows that 

 this spot must be a kind of organ. The brownish chitine 

 around the whitish spot (PI. 4. fig. 8) is glabrous, without the 

 numerous irregular impressed points adorning nearly the whole 

 surface ; the spot itself is slightly arched, presenting a small 

 central oblong impression, and on each half a very small group of 

 very fine impressed dots. I know nothing of the nature of this 

 organ. It is probably homologous with the curious organ pointed 

 out on the upper surface of the head of Anaspides Tasmanice, 

 G. M. Thoms., by W. T. Caiman (Caiman, "On the Genus 

 Anaspides, &c.," Trans. Eoy. Soc. Edinburgh, vol. xxxviii. partiv. 

 1896, p. 788). I have searched for this organ on a few species of 

 Girolana, and found a vestige of it in Cir. horealis, Lilljeb. I 

 hope in the near future to publish a note on the two organs in 

 various Malacostraca. 



Antennulce. — Bouvier has made an interesting discovery : he 

 points out the existence of an accessory ramus originating from 

 the third joint of the peduncle of the antennulse, and consisting 

 of only one very small joint. I can only confirm his description. 

 I have now looked in vain for an accessory ramus in some species 

 of Girolana ; so far as I know, it has not been observed in any 

 other Isopod, but it is well developed in Apseudes and the major 

 part of AmpMpoda G-ammaridea. The short setae on the joints 

 of the flagellum mentioned by Bouvier (p. 144) are the sensory 

 (olfactory) organs. 



Antennce. — The Erench author writes (p. 144) : — " Les pedon- 

 cules antennaires (pi. iv. fig. 7), comme dans la plupart des 



