72 TWELFTH ANNUAL REPORT. 



sensory bristle near the base in front and two bristles a third from 

 the end; the second antennae are furnished with a powerful basal 

 joint, while each of the main subdivisions of the rami has its bristle, 

 which are nearly equal; two of the terminal setae are toothed for 

 the basal half and pectinate distally, but the others are feathered 

 throughout; the four- join ted ramus has a spine on the second joint 

 and a longer one at the end, and all the joints of both rami are orna- 

 mented with triple series of spines; the maxillae are three-spined at 

 the end and are in almost constant motion; the first pairs of feet 

 have curious comb-like bunches on some of the setae; the abdomen 

 is very short and terminates in inconspicuous teeth, the posterior 

 part of the abdomen being ornamented with teeth flattened longi- 

 tudinally so as to look like spines from the side; the last foot is 

 simple but bears a large appendage; the posterior third of the shell 

 is fringed by extremely minute spines, but anteriorly by lanceolate 

 stiff spines flattened longitudinally like the spines of the abdomen; 

 the caudal setae are seated on a high prominence of the abdomen, 

 and are fringed along their whole length, not merely at the end. 

 The female is 1 mm. long, the male 0.5 — 0.6 mm., in which sex the 

 antennules have more numerous lateral bristles, the first foot has 

 a claw and the back is less elevated. The semen bodies are irre- 

 gularly round with small nuclei. 



III. Genus Streblocercus, Sars. 



In form like Macrothrix laticornis, head terminating in a long 

 rostrum bearing the long, twisted antennules. Antennules very 

 large, curved backward and outward. Head not separated by a 

 destinct depression from the body, very high, slightly arched above, 

 abrubtly curved below with spines upon the margins. The anten- 

 nae are large; four-jointed ramus much the longer, with four setae. 

 Labrum with a large process. Post-abdomen as in Macrothrix lati- 

 cornis. Eye near the beak ; pigment fleck small, below it at the 

 base of the antennules. Length .33 mm. S, minutus is the only 

 species. 



Our Macrothrix pauper seems a near approach to this genus; 

 both have a strong spine or claw on the first foot which projects 

 beyond the shell, but there are many differences. M. pauper is 

 1 mm. long. 



