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



The third and fourth pairs carry similar branchial plumes to the second ; but the 

 fifth pair is shorter than any of the preceding pereiopoda, and has no branchia attached 

 except a small pleurobranchial plume. The whole may be tabulated as follows : — 



Pleurobranchise, 

 Arthrobranchise, 

 Podobranchis, 

 Mastigobranchiae, 



The first pair of pleopoda in this specimen, which is a female, is small and feeble. 

 The second is biramose, and the inner branch carries a single stylamblys fringed with 

 ciliated hairs, as do all the other pairs of pleopoda until the sixth, which forms part of 

 the rhipidura. 



Observations. — The first specimen of this species, which was not a very perfect 

 one, was taken south-east of the Philippine Islands, at about seventeen degrees west 

 and seven degrees north of where Pentacheles obscura was taken. 



The second specimen was taken near Juan Fernandez, at three times the depth, on 

 a similar bottom but at a temperature six degrees lower. 



The two localities of this species, being more than ten thousand miles apart, induced 

 me to compare the specimens with great care. 



Pentacheles gracilis, n. sp. (PI. XVI. figs. 1, 2). 



Carapace long-ovate ; anterior margin furnished with two sharp rostral teeth directed 

 obliquely upwards ; a similar strong, sharp tooth is directed forwards at the inner angle 

 of the orbit. Outside the orbital notch is a similar tooth directed obliquely inwards, 

 beyond which the lateral angle of the carapace projects anteriorly in the form of a 

 strong, sharp tooth, passing oblicpxely upwards, outwards, and anteriorly beyond the 

 extremity of the median or rostral teeth. The lateral margins of the carapace are evenly 

 denticulate, and divided at the cervical and hepatic fissures. There are ten teeth on 

 the anterior, three on the median or hepatic, and fourteen on the posterior or branchial 

 margins. These last lessen in size as they proceed posteriorly. Between the several 

 teeth are a few hairs. The median dorsal ridge is armed with a row of single teeth, 

 gradually decreasing in size as they proceed posteriorly. The general surface is polished 

 and sparsely covered by small granular points, from which spring short, curved 

 hairs ; the branchial region is clearly defined by a baccate or minutely denticulate 

 line. 



