134 discovery reports 



Occurrence : 



St. 250. 17. vi. 27 (night). East of Tristan da Cunha, 30o(-o) m., 4 imm. c?c?, 6—6-5 mm -! J adult $, 8 mm., 



4 imm. $$, 4-5 mm., 4 very small juv. 

 St. 257. 24. vi. 27 (night). West of Cape of Good Hope, 25o(-o) m., 3 juv. 3-5 mm. 

 St. 266. 21. vii. 27 (night). West of Orange River estuary, 20o(-o) m., 1 <$, 7 mm., 1 juv., 5 mm.; 4 juv. $$, 4-5- 



5-5 mm. 

 St. 267. 23. vii. 27 (night). North-west of Angra Pequena, 550-45o(-o) m., 1 imm. <$, 4-5 mm. 



Remarks. These specimens do not differ in any essential from the published descriptions of the 

 species, except that the uropods are proportionally longer in comparison with the telson. Illig (1930, 

 p. 452) says that the endopod of the uropod is three times as long as the telson and that the exopod 

 is slightly longer. I find in the largest of my specimens that the endopod of the uropod is fully four 

 times as long as the telson. 



None of my specimens is fully mature and all are badly damaged. Only one or two possess any 

 thoracic appendages and only a few have any eyes. It is evidently a very fragile form and I think that 

 this fragility is responsible for the difference of opinion, which has arisen among workers, as to 

 whether the median setae on the telson are plumose or not. Only in two specimens of this collection 

 are there any complete setae on the telson — one on each animal. When closely examined with a high 

 power both these proved to be very sparsely and delicately plumose. I think that in all probability 

 they are normally plumose, but that the fragility, which is evident in the rest of the body, extends also 

 to the armature of the setae, so that where they appear to be non-plumose they have in fact been 

 stripped bare of their armature. 



Illig, in his description of the type, stated that there were five thorns on the inner margin of the 

 endopod of the uropod. Zimmer (1914, p. 395) recorded that he could find no trace of these in his 

 specimens and I could find none in any of my specimens either. 



Distribution. This is one of the few species of mysids which are represented in the fauna of both 

 the northern and the southern hemispheres. It was first recorded from the Mediterranean by Lo 

 Bianco as Enchaetomera tenuis and was later found in the same area from depths of 900-2500 m. and 

 100-800 m. (Tattersall, 1909; Colosi, 1929). Illig's types were collected in the Indian Ocean and he 

 recorded (1930) the species again from four stations in the Indian Ocean in vertical hauls from 600 m. 

 and 3000 m. In the Atlantic it has been recorded from equatorial waters and from the Gulf of Guinea in 

 vertical hauls over great depths ; there have also been a number of records from deep water in the South 

 Atlantic. W. M. Tattersall (1943) recorded it from the East Pacific west of San Francisco from 100 m. 



It is evidently a somewhat bathypelagic form, but as previously it has always been recorded from 

 vertical hauls with open nets, it is not possible to say at what depths it normally lives. The three hauls 

 in which it appears in the Discovery collection were all taken at much shallower depths than earlier 

 records and in each case the net failed to close. These three hauls were taken at night and it may well 

 be that these animals, in common with so many other species of mysids, carry out an upward migration 

 during the hours of darkness. 



Genus Caesaromysis Ortmann, 1893 

 1893 Caesaromysis Ortmann, p. 22. 



This genus was instituted by Ortmann for a new species, C. hispida, for specimens taken in equa- 

 torial waters in mid-Atlantic. He defined the genus as possessing the following characters : 



(1) Very long thorn-like rostral projection. 



(2) Very plump body armed profusely with very long, strong thorns. 



(3) Eyes large, with two areas of ocelli and long slender stalks. 



