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



the typical species, entire, but deeply cleft in the middle, the incision being rather 

 narrow, and occupying about one-fourth of the length of the telson. The terminal 

 lobes are pointed and densely spinulose at their inner edge, and also furnished at the 

 tip with a few denticles of the same appearance as those occurring along the lateral 

 edfres. 



The uropoda (see fig. 23) had the terminal part of both plates broken off in the 

 specimen examined, and their respective lengths cannot therefore be given. The 

 auditory apparatus within the base of the inner plate is well developed, with the otolith 

 rather laroe and slobidar. 



Habitat. — The above described specimen was taken at the entrance of Port Philip, 

 South Australia, along with the specimens of Anchialus angustus. The locality is : — 



Station 161, April 1, 1874; lat. 38° 22' S., long. 144° 36' E.; depth, 33 fathoms; 

 sand. 



Genus 7. Siriella, Dana, 1852. 



Siriella, Bana, United States Exploring Expedition, Crustacea, pt. i. 

 Cijiitliid, Thompson (male). 



Generic Characters. — Form of body more or less slender. Carapace very small, not 

 nearly covering the whole of the trunk ; frontal margin produced in the middle. Eyes 

 normally developed. Antennular peduncle rather elongate ; male appendage but slightly 

 prominent, issuing from lower face of terminal joint. Antennal scale with outer edge 

 naked, and terminating in a small dentiform projection, apex obliquely truncate. 

 Mandibles with molar protuberance imperfectly developed. Second pair of maxillae 

 having but two masticatory lobes ; terminal joint of palp large and oblong, not incurved. 

 Legs subequal, rather stout, with propodal joint entire or subdivided into two articula- 

 tions only, and having a double row of densely crowded apical bristles ; terminal joint 

 forming a very strong falciform claw. Caudal limbs in male natatory, basal lobe of inner 

 branch usually transformed into two gill-like, more or less spirally twisted stems. Telson 

 elongate, densely spinose at the edges, apex entire, not incised. Outer plate of uropoda 

 broader than inner, and having an imperfect articulation at apex, outer edge partly 

 spinous. Auditory apparatus well developed. 



Remarks. — The present genus is chiefly characterised by the structure of the legs, 

 which are more decidedly imguiculate than in any other known genus of Mysidans, 

 turther by the caudal limbs in the male having the basal expansion of the inner branch 

 converted into peculiar gill-like appendages, finally by the structure of the telson and the 

 outer plate of the uropoda. The genus is represented in most tracts of the ocean, and 

 comprises about ten different species, the greater part of which would seem to lead a true 

 pelagic existence, being met with at the surface of the sea, far from the coasts. The 



