MYSIDACEAN CRUSTACEANS TATTERSALL 541 



small and slender. Apical spines are long and strong. The apical 

 plate is not produced at all and is armed with 9-13 spinules, which 

 are usually uneven in size and consist of somewhat larger ones alter- 

 nating with smaller ones in the spaces between them (fig. 5/). 



In some of the specimens the proximal spine on each lateral margin 

 is so small that only by the slight indentation of the margin at the 

 point of its origin can one be led to see it. Fage mentioned a similar 

 condition in his description of the types of L. schmidti. 



These Hawaiian specimens are somewhat smaller than the tj'pes 

 and paratypes collected by the Dana. The one ovigerous female in 

 this collection was carrying advanced embryos, but it measures only 

 15 mm., whereas those of the Dana were from 17-20 mm. in length. 

 Apart from this slight difference, the present specimens differ in only 

 one character from the full description given by Fage (1942, p. 35) — 

 the form of the lamina from the antennular peduncle. He made a 

 strong point of the fact that in all his specimens the anterior margin 

 of this lamina was evenly rounded and without teeth or spinules. 

 The only armature he figured was a single slender simple seta in the 

 middle of the apex. In all the Hawaiian specimens the inner margin 

 ends in a strong tooth. The tooth is separated by a small concavity 

 from the rounded apex, which extends only very slightly beyond it. 

 From three to five very minute notches can be made out on the inner 

 half of the apex, but the other half and the whole of the outer margin 

 are completely smooth. In the immature specimens the inner margin 

 and the inner half of the apex are adorned with a few regular very fine 

 setae. It may be that the small notches seen on the margins of the 

 older specimens indicate the positions from which setae had arisen and 

 have subsequently been lost. 



Fage considered that the form of the antennular laminae was of 

 specific importance but, though differing in this particular character, 

 the present specimens agree so very closely with L. schmidti in all 

 other characters that they should be referred to this species. It may 

 be that they represent a geographical race of L. schmidti. 



If my diagnosis is correct, the geographical range of this species 

 is considerably extended northward and eastward. The captures off 

 Hawaii were made in precisely the same conditions as the captures 

 from north and west of New Guinea (Fage) and the western Arabian 

 Sea (O. S. Tattersall) — that is, the animals were pelagic in depths of 

 not more than 550 m. from the surface over much greater depths. 

 Possibly the species is widely distributed in similar conditions through- 

 out the tropical Pacific. 



The adult female described below as Lophogaster sp. B closely re- 

 sembles schmidti in the form of the rostral plate, the length of the 

 alar spines, and the armature of the lateral margins of the telson. 



