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



of pereiopoda being broken off, we can only be certain whether it belongs to the 

 Polycarpidea or the Monocarpidea by consideration of the value of certain structural 

 details. Thus the mandibles agree with those of Campylonotus and differ from those of 

 Chorismus and Merhippolyte. The ventral surface of the pereion corresponds generically 

 with Campylonotus, although it differs specifically from Campylonotus semistriatus in 

 having a pair of teeth between the second pereiopods only, whereas in Campylonotus 

 semistriatus there is a pair between the first as well as the second pair of limbs, but in 

 Chorismus and Merhippolyte there are none. On these grounds it seems more likely to 

 belong to the Monocarpidea than to the Polycarpidea. 



Our specimen was a solitary one among a large number of Campylonotus 

 semistriatus. 



Palaemon, Fabricius. 



Palxmon, Fabricius, Suppl. Entom. Syst., p. 402. 



„ Leach, Malacos. Pod. Brit., pi. xiv. 

 Palemon, Milne-Edwards, Hist. Nat. Crust., torn. ii. p. 387. 

 Leander, Desmarest, Ann. Soc. Entom. France, torn. vii. ser. 2, p. 87, 1849. 



„ Stimpson, Proc. Acad. Nat. Sci. Philad., p. 109, 1860. 



Carapace less than a third the length of the animal, posteriorly smooth, rounded, 

 slightly compressed anteriorly, elevated into a crest over the frontal region, and 

 produced to a long, laterally compressed rostrum that is armed above and below with 

 teeth varying in number according to the species. The orbital notch is well defined, 

 but has no tooth. At the outer can thus a strong first antennal tooth projects ; below 

 it and still further down a second tooth stands within the margin on a level with 

 the second pair of antennae, and above the line of the fronto -lateral angle (" spina 

 branchiostegiana " of Stimpson). There is no tooth on the hepatic region, but a 

 depression or fissure thence to the upper side of the inferior marginal tooth is 

 conspicuous. 



The pleon is smooth, and like the carapace dorsally rounded and laterally 

 compressed. 



The telson is similarly characterised, tapers gradually to a central tooth, and is 

 furnished with dorso-lateral spines. 



The ophthalmopoda are short, broad, uniarticulate, and supported on a slender 

 pedicle ; the ophthalmus is hemispherical, and has an ocellus that is sometimes distinct, 

 but in the typical species is involved within its margin. 



The first pair of antennae has the first joint compressed above and beneath, and 

 armed on the outer margin with a sharp, short stylocerite, and at the anterior distal 

 angle with a strong flattened tooth ; the second joint is thicker than the first, 

 shorter on the upper surface than on the lower, and articulates obliquely with the third 



