66 DISCOVERY REPORTS 



of these apical spines. The outermost pair is extremely long, measuring rather more than one-third 

 of the length of the telson, the next two pairs are progressively shorter and the inner two pairs are 

 small and almost equal in length. Illig figures these spines as much smaller, the longest being less than 

 one-fourth of the length of the telson, and he describes and figures three pairs of very small spines 

 along the middle of the apex flanking the median spine, making six pairs in all. All these apical spines 

 are finely spinulose in the Discovery specimen. 



Tattersall (1939, p. 230, text-fig. 3) referred an immature specimen 

 of 7 mm., taken from N.E. of Seychelles, to this species. In his 

 specimen the apex of the telson was truncate with no trace of 

 emargination. It bore five pairs of spines like the Discovery 

 specimen but the outer two pairs were almost equal in length, 

 while the inner three pairs were all of equal length and very small 

 with plumose setae in the spaces between them (Fig. 10). 



The Discovery specimen measures 9-6 mm. The brood lamellae 

 are not yet developed and the differences it shows from Tattersall's 

 smaller specimen and from the adult of Illig are due probably to 

 growth changes. 



The eyes are well developed with normal ocelli and a golden 

 brown pigment. They appear to be somewhat shorter and thicker than those figured by Illig. I am 

 unable to make out the small finger-like process which Tattersall recorded on the inner face of the eye. 



Distribution. With the exception of the one record by Tattersall (1937, p. 1) from the Caribbean 

 Sea, all records of this species are from deep water in the Indian Ocean near Aden or from the N.E. 

 of Seychelles. The Discovery specimen was taken in much shallower water at a depth of 550-0 m., 

 at station 1586 half-way between Seychelles and Obbia on the coast of Africa. 



Fig. 10. Petalophthalmus ocalatus Illig. 

 Telson and uropods of female in dorsal 

 view, x 26. 



1869 



1873 

 1883 

 1896 



Family Mysidae 



Subfamily BoREOMYSINAE 



Genus Boreomysis G. O. Sars, 1869 



Boreomysis G. O Sars, p. 330. 

 Petalophthalmus (pars), W.-Suhm, p. 40, figs. 

 Arctomysis Czerniavsky, p. 8. 

 Pseudanchialus Caullery, p. 368. 



Remarks. Seven of the species which have been referred to the genus Boreomysis are represented 

 in the Discovery collections. In addition I am obliged to add five new species, B. illigi, B. acuminata, 

 B. tattersalli, B. insolita and B. bispinosa. There has been, and still is, much confusion in this difficult 

 genus due, to some extent, to the fact that several of the described species have been founded on one, 

 or possibly two, immature individuals. A close study of the genus proves that there is considerable 

 variation among its members and, unless a very large number of species is to be erected, the species 

 must be defined along broad lines, with a good deal of latitude allowed as regards minor features. The 

 species B. rostrata is an outstanding example (see p. 70). 



I accept the suggestions of previous workers that the following synonymies occur in the genus: 



B. sibogae Hansen = B. spinifera Coifmann. 



B. calif ornica Ortmann = B. media Hansen = l B. kinkaidi Banner. 

 B. rostrata (pars) Illig = 5. inermis Hansen. 

 B. arctica (Kroyer) = fi. tregouboffi Bacesco. 

 1 See footnote on page 67. 



