90 THE VOYAGE OF H.M.S. CHALLENGER. 



form of Euphausiidaj. On closer examination, however, I felt convinced of its consti- 

 tuting a new and peculiar species of the genus Eitphcmsia, that retained, so to speak, in 

 the adult state, certain apparently larval characteristics. After the plate had been 

 printed, I found among specimens of Euphausiidae from Port Jackson, a few male 

 examples of somewhat larger size than the one here figured, but, for the rest, closely 

 agreeing with it in all essential characters. The most striking feature in the present 

 species is unquestionably the very peculiar form of the frontal projection, from which 

 character, indeed, the specific denomination has been derived. 



Description. — None of the specimens exceed a length of 8 mm., most indeed are 

 rather smaller, and hence the species may be regarded as a true pigmy form. 



The body (see PI. XVI. fig. 17) is rather short, the tail measuring about twice the 

 length of the anterior division. 



The carapace has no trace of lateral denticles, the inferior margin being quite smooth 

 and slightly incurved. The anterior part does not exhibit any distinct keel above ; it 

 projects as a broad, well nigh quadrate plate, arching over the base of the eyes, and 

 reaching about the middle of the basal joint of the antennuhie. This plate, too, is slightly 

 hollowed along the middle, and at the apex abruptly truncate, or sometimes even slightly 

 emarginate, with distinctly projecting lateral corners. 



The caudal segments are smooth above and provided with comparatively small, 

 rounded epimera. The last segment is a trifle more elongate than the preceding, and 

 juts out at the end above as a small dentiform projection (see fig. 22). The preanal 

 spine is very small, and unguiform. 



The eyes (see fig. 18) exhibit a somewhat clavate form, having their greatest 

 thickness in the middle of the pedicle, the cornea not being at all expanded. 



The antennular peduncle (ibid.) is provided at the end of the basal joint above, with 

 a very thin and membranous lobe (see fig. 19), serrate at the edge and overlaj^ping the 

 base of the succeeding joint. The outer corner of the basal joint is, moreover, drawn 

 out to a strong, anteriorly pointing spiiie. 



The antennal scale (see fig. 18) scarcely projects beyond the second joint of the 

 antennular peduncle, and exhibits an oblong-ovate form, with the apex narrowly 

 rounded and the outer corner drawn out to a distinct, although short, dentiform 

 projection. 



The oral parts and the legs do not seem to exhibit any essential structural pecu- 

 liarities. 



The gills are, on the whole, not particularly] developed, the digitate lobules being 

 in comparison few in number and the posterior pairs but slightly arborescent. 



The copulatory appendages to the first pair of pleopoda in the male (see fig. 20) diff"er 

 somewhat in structure from those in other species of the family, being, on the whole, 

 much simpler, and without the strong hamiform processes generally observed. They 



