MUSEUM OF COMPARATIVE ZOOLOGY. 



567 



of the lateral spines is variable. In specimens from the deeper soundings 

 they are much longer than in those from shallower depths. The specimens 

 from 66 fathoms measure 10 mm - between the tips of the fourth pair of spines ; 

 length of a single spine, 4 mm -; from front of head to end of telson, 8 mm - 

 Average specimens from Achacache, 11 fathoms, measure 7 mm - from tip to 

 tip of fourth pair of spines ; 9 mm - from front of head to end of telson. The 

 former are also lighter colored and more transparent than the latter. Many 

 of the females are with eggs under the thorax. 



Allorchestes echinus, sp. nov. 



Fig. 19 



Tigs. 19-21. Allorchestes echinus : 19. Female (nat. s. 6mm.). _ 20. Vertical section of body (4th 

 thoracic segment). — 21. 2d thoracic leg of male. % 



Body short and very stout, with four longitudinal rows of spines. One 

 row on each side of the median line of the back ; each spine of this row 

 arises from the hind margin of the terga of the first thoracic to the fourth 

 abdominal segment inclusive. Another row of eight smaller spines lower 

 down on each side of the body ; these arise from the terga of the first thora- 

 cic to the first abdominal segments inclusive, near their line of junction with 

 the epimera. Slight projection downward and forward from front margin 

 of the head between the first antennae ; a tubercle on each side below the 

 eyes. Eyes round, large, somewhat protuberant. Epimera of first four 

 thoracic segments large, triangular, their apices directed downward ; a ridge 

 extends from the base down through the centre of each of these epimera to 

 the apex. The fourth epimeron has beside the ridge a small tubercle on the 

 hind margin. Fifth epimeron bilobed, with a tubercle on each lobe. Telson 

 entire. 



Flagellum of first antenna composed of six to eight segments. Basal 

 joint of second antenna swollen and distinct from the head; olfactory den- 



