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



The branchiae consist of five pleurobranchial, five arthrobranchial, and one podobranchial 

 plumes, as shown in the following table : — 



Pleurobranchise, 

 Arthrobranchiae, 

 Podobrancliias, 

 Mastigobranchiae, . 



In its branchial arrangement it agrees with Acanthephyra and Notostomus. 



Geographical Distribution. — The original specimens described by Milne-Edwards 

 were received from New Guinea, and those of the Challenger were taken off the Fiji, 

 Philippine, and Admiralty Islands. Another species has been described by A. Milne- 

 Edwards, from a specimen taken off the Island of St. Domingo. 



Observations. — This genus is a very interesting one. Judging from their appear- 

 ance, the species are active and pugnacious animals. The long, sharp, and bayonet- 

 like scaphocerites must be capable of inflicting a deep wound, and their power is increased 

 by the serrate condition of the outer margin, a feature that is seen in Thalassocaris also. 

 Their power of progression must also be great, as may be seen from an examination 

 of the leading features. The teeth upon the dorsal surface of the pleon can be tightly 

 compressed against the body ; the appendages not utilized are capable of being drawn 

 close to the animal, and its narrow form and polished sides seem fitted to enable it to 

 shoot through the water. With the rostrum and outstretched scaphocerites it will be 

 capable of a formidable attack on animals larger than itself. In regard to its power of 

 defence the dermal tissue is strong and rigid, and when at rest with the pleon curved 

 under the ventral surface, the dorsal teeth extended, and the scaphocerites and rostrum 

 pointed outwards and forwards, it cannot be easily approached, and by the manner in 

 which the posterior teeth on the lateral margins of the carapace are supported by those 

 on the lower margin of the first somite of the pleon, the animal appears to be capable of 

 resisting a strong charge from an attacking enemy. 



Oplophorus typus, Mdne-Edwards (PL CXXVII. fig. 1). 



Oplophorus typus, Milne-Edwards, Hist. Nat. Crust., torn. ii. p. 424, pi. xxv. bis, figs. 6, 7. 



Eostrum subequal in length with the carapace, armed on the upper surface with 

 six small teeth and on the lower with seven. 1 The tooth at the infero-posterior angle 

 of the carapace is directed obliquely backwards and outwards. 



Pleon subcarinated ; posterior margin of the first two somites rounded, that of the 

 three following produced into long and sharp-pointed teeth. Anterior margin of the 



1 Milne-Edwards says seven or eight little teeth on each border, but as some of them are rudimentary the number 

 probably varies. 



