44 DR. R. V. WILLEMOES-SUHM ON SOME ATLANTIC 



The male differs from the female by the rudimentary condition of its carapace and the 

 metamorphosis of the first antennse } the palpus mandibularis, the maxilliped, and first 

 gnathopod into prehensile organs. 



Petalophthalmus armiger, n. sp. 



Eyes wanting. Eyestalks with spherical concave terminations at the place where one 

 would expect to find the eyes. Length 37-44 millims. 



Habits of Life, and Colour. 



Petalophthalmus is a member of that deep-sea fauna which we sketched when de- 

 scribing Gnathophausia zoea, in which, however, it seems not to be common. Its colour 

 is a bright red. 



We have now described (1) a lophogastriform genus (Gnathophausia), with three 

 species, (2) a genus allied to the former, but forming a new family (Chakwaspis),&n& (3) 

 a Mysidiform genus (Petalophthalmus) — all of which have a free carapace and certain 

 peculiarities which show that their existence dates from a period in which the family 

 characters of Schizopods were not so sharply defined as they are now. They are pre- 

 cursors of the Mysidse and Lophogastridse, and representatives of another family, having 

 characters which, among the Schizopods, are only shared by Nebalia, but in all other 

 respects entirely different from tbis genus. Now the idea presents itself whether it would 

 be advisable to bring all these Schizopods together into one group, the chief and only 

 universal character of which would be that they all have a free dorsal shield. "We could 

 best describe this in the following synoptical way : — 



fQ abdominal segments, palpus maxilla prima? Nebalia. 



| f 7 legs, subjoints, palpus maxillae prima?, supple- 

 Group I. | mentary eyes, Lophogastriform Gnathophausia. 



Dorsal shield free. K 7 ohrlnmiTinl <*pp-- ' . _ , , . 



I 7 aDClommal se S" J 6 legs, no subjoints, 7 breeding-lamellae, Mysi- 



ments. 



Group II. 



Dorsal shield fas 



diform ' Petalophthalmtts. 



i^ 4 legs, no subjoints, branchiae as in Lophogaster . . Chalaeaspis. 



f 7 legs, no subjoints, no palpus maxillae prima?, 



no supplementary eyes Lophogastek. 



7 abdominal seg- 



. , ,iim.>m. 1..,. 1 ■ , 6 legs, -with or without subjoints, 2 breeding- 



tened to the ^ ments> < lamella? Mtsis and Sieiella. 



pereion. 



I 8 legs (the last wanting or rudimentary), branchiae 



^ free, supplementary eyes Etjphausia. 



This arrangement of the Schizopods would, no doubt, have a certain advantage, as it 

 prevents the destruction of the family characters of our old and well-known forms in 

 favour of a few deep-sea genera, all of which have a certain peculiarity wbich they share 

 only with Nebalia. But it is not a natural genealogical arrangement ; for, from what 

 has been said, there is no doubt that Gnathophausia is, if I may use the expression, ah 

 ancient Lophogaster, and Petalophthalmus an ancient Mysis. I therefore propose to 



