1198 THE VOYAGE OF H.M.S. CHALLENGER. 



Laetmatophilus purus, n. sp. (PI. CXXXIL). 



The front of the head somewhat produced, with a small pointed process in advance 

 of the eyes on each side ; the lower part emarginate for the insertion of the lower 

 antennae to the rear of the upper ; the head with a small dorsal depression to the rear ; 

 the first five segments of the perseon each with a dorsal depression, giving the back a 

 corruo-ated appearance ; the third segment has a small ventral process at about the 

 middle, and the second segment is a little produced ventrally, but not into a definite 

 process ; the fourth segment of the pleon is a little longer than any of the preceding 

 segments, narrow, cylindrical ; the following segment is very short, None of the side- 

 plates are deep ; the branchial vesicles on the second to the sixth perseon-segments are 

 strongly bent forward, the pair attached to the second gnathopods being much smaller 

 than the following pairs. 



Eyes round, prominent on special lobes ; retaining a dark colour in the specimen 

 mounted in Canada balsam ; the outer ring of ocelli contained thirty. 



Upper Antennae. — The first joint shorter than the head ; the second thinner but 

 much longer, the under margin fringed with long setiform spines ; the third joint a 

 little shorter and thinner, similarly furnished ; the flagellum of three joints, together 

 not quite so long as the third joint of the peduncle, similarly armed, the first joint 

 much longer than the other two united, the second twice as long as the third. 



Lower Antennae stouter and much longer than the upper ; the first two joints 

 short, the gland-cone small ; the third joint not long, rather thick ; the fourth joint 

 thinner than the preceding, as long as the second joint of the upper antennse, with 

 slender spines on the lower margin, some shorter and stronger spines on the upper, and 

 some lateral groups; the fifth joint considerably longer than the fourth, with many 

 spines on the lower margin ; the flagellum practically of one thick joint, narrowing 

 only near the apex, a little more than half the length of the fifth joint of the peduncle, 

 with short spines of various thicknesses distributed about it, including two curved ones 

 on the apex ; the apex under a high power appearing to consist of two minute joints 

 scarcely distinct from the large one. 



Upper Lip. — The distal margin is here, if I am not mistaken, rather deeply but not 

 broadly emarginate ; but in Laetmatophilus tuberculatus Boeck says that the upper lip is 

 distally rounded (paa Enden afrundet). 



Mandibles not well observed ; molar tubercle prominent, palp nearly as in Platophium 

 dame. 



Lower Lip. — Principal lobes broad, the convex distal and sinuous inner margins 

 meeting in a small projecting lobe ; the mandibular processes rather long, divergent, 

 apically narrowed. 



First Maxillse. — Inner plate inconspicuous ; outer plate apparently with nine spines 



