66 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 5 



right wanting in the holotype specimen. A smaller spine on the pos- 

 terior border at the mid-point, in front of it a boss or tubercle at the 

 intestinal level. A total of eight major prominences, with the two epi- 

 gastric, ten. Rostral spines long, cylindrical, tapering, not flattened, 

 contiguous from bases almost to tips, which are sharply divergent, except 

 in young specimens; length of rostrum about four-fifths times the dis- 

 tance between the preorbital spines. Orbits tubular, protruding beyond 

 margins of carapace, postorbital extending beyond preorbital, their tips 

 making a straight line with the tip of the antennal spine when seen in 

 dorsal view. Upper orbital margin deeply incised, spines separated by a 

 fissure fused distally but open proximally and extending on to the 

 hepatic region. 



Basal antennal article broad, bearing an obliquely directed spine. 

 Flagellum long, reaching four fifths the length of the rostrum, its first 

 two movable segments appreciably thickened. A tubercle at the level of 

 the green-gland opening; a similar pterygostomian tubercle. Merus of 

 third maxilliped irregular in outline, anterointernal angle sharply pro- 

 duced, anteroexternal angle broadly lobate, merus inserting at a point 

 considerably below the distal extremity of the ischium. 



First ambulatory leg much the longest in the male, the remaining 

 legs gradually diminishing; those of the female rather short; legs cylin- 

 drical, pubescent, somewhat nodose. Carpus slightly inflated and grooved 

 superiorly; dactylus with lower border spinulous, tip yellow and in- 

 curving. 



Distribution: In addition to the type series from Isabel Island, 

 Mexico, a female specimen was dredged by Velero III at Playa Blanca, 

 Costa Rica, and a young male at La Libertad, Ecuador. 



Remarks: The proposed species is the Pacific counterpart of M. 

 trispinosum (Latreille) (1825), from which it may be separated by 

 the following features: 



(1) The rostral horns are long, cylindrical, and contiguous 

 throughout the greater part of their length, instead of short, 

 flattened, and diverging almost from their bases. 



(2) The preorbital spine is directed obliquely forward instead of 

 transversely. 



(3) The first two movable segments of the antenna are coarse 

 instead of slender. 



(4) The postlateral spines are more backward than sideward 

 pointing. 



