24 University of California Publications in Zoology [Vol. 23 



Gennadus borealis Kathbun 



Gennadus borealis Eathbun, Proc. U. S. Nat. Mus., 24, 887, 1902; H. A. E., 

 10, 147, figs. 88 and 89, 1904. 



Fig. 11. Gennadas borealis; a, lateral view of carapace, J, X 2; b, thelycum, 

 X 5; o, petasma, X 5; d, foot of first pair, c?, X 3 (Eathbun, U. S. N. M.). 



Characters. — Eostrum reaching at least half way along the eye-stalk, some- 

 times to the cornea, armed with a single tooth; carina very distinct nearly to the 

 posterior margin of the carapace, but sharpest in front of the cervical groove; 

 a sharp marginal spine at the angle of the antero-lateral sinus. Byes light brown, 

 globular, having a speck of black pigment near their base on the outer margin 

 of the stalk; tubercle large and acute. Antennal scale extends beyond the anten- 

 nular peduncle by about the length of the last segment of the peduncle. Chelae 

 of first pair of feet narrow and elongate, as in the succeeding pairs. 



Thelycumi consisting of a horizontal, convex, subtriangular plate, or tubercle, 

 placed between the third pair of legs, followed by two transverse plates between 

 the fourth and fifth pairs. The anterior of these two plates is subquadrilateral, 

 narrowest in front; the posterior plate is somewhat fan-shaped, narrow behind, 

 its anterior margin rounding and with a blunt median point. The andricum or 

 petasma 2 consists of a pair of small leaves not in contact, each of which is 

 attached at its proximal end; at extremities of distal margin are two lobes or 

 teeth, the outer of which is curved; the inner portion is partially folded to form 

 an irregular longitudinal plate. 



Exopodites of first abdominal appendages not so long as the carapace ; between 

 the bases of these appendages is a sharp spine, equally developed in both sexes. 



Sixth abdominal somite carinate, more than twice as long as fifth; telson with 

 a small lateral spine at its posterior fourth, two spines at tip. 



Dimensions.- — Type, male: length of carapace and rostrum 13.6 mm., of 

 abdomen on middle line 29 mm. ; female : length of carapace and rostrum 18 mm., 

 of abdomen on middle line 37 mm. 



Type Locality. — Off Copper Island, Kamchatka, 1567 fathoms ("Albatross" 

 station 3783). 



Distribution. — Also taken by the ' ' Albatross ' ' from north of Eat Islands, 

 Aleutians, to off South Coronado Island, Lower California, 266 to 2182 fathoms. 



Remarks. — Very near G. parvus Bate, but differs in the longer rostrum, the 

 presence of a lateral spine on the telson, the greater length of the antennal scale, 

 the elongated chelae of the first pair of feet, and the different form of the 

 thelycum and andricum or petasma (Eathbun). 



1 An accessory reproductive structure on the ventral surface of the cephalo- 

 thorax peculiar to the female. 



2 A membranous accessory reproductive structure attached to the first pair of 

 pleopods of the male. 



