346 PERCY SLADEN TRUST EXPEDITION 



230 fathoms. ' Most of the subfamily are to some extent cryptozoic, and a great many 

 actually commensal. A sketch of the distribution of this habit within the group has 

 already been given on pp. 329, 330. Unfortunately, little is known of the behaviour of 

 the Pontoniinse or of their relation to the animals which serve as their hosts. A detailed 

 study of this subject, which could only be made in the field, would undoubtedly give 

 very interesting results. 



The Genera of the Pontoniinae. 



The genera of the Pontoniinae may be briefly characterized by means of a key, as 

 follows : 



I. Body very slender and compressed. Thorax without swelling. 6th abdominal 

 segment much elongate. Outer flagellum of antennule deeply cleft. A gill may be 

 present, on the second maxilliped. 



A. Mandibular palp present. Gill on second maxilliped. Rostrum toothed 



below. 



Urocaridella Borradaile, 1915. 



B. No mandibular palp. No gill on second maxilliped. Rostrum without teeth 



below. 



Urocaris Stimpson, 1860. 



II. Body moderately stout, not compressed. Thorax of female swollen dorsally. 

 6th abdominal segment short. Outer flagellum of antennule deeply cleft. A gill may 

 be present on the second maxilliped. [No mandibular palp.] 



Ancyclocaris Schenkel, 1902. 



III. Body never very slender, or much compressed. Thorax without swelling. 

 6th abdominal segment never much elongate. Outer flagellum of antennule rarely deeply 

 cleft. No gill on second maxilliped. 



A. Mandibular palp present. 



PaloBmonella Dana, 1852. 



B. No mandibular palp. 



1. Scale of second antenna rudimentary. 



Typton Costa, 1844. 



2. Scale of second antenna well developed. 



i. Gracefully-built forms, with body little if at all depressed, rostrum well 

 developed, and almost always toothed, slender legs, whose dactylo- 

 podites are usually narrow and never hook-like, and antepenultimate 

 joint of third maxilliped narrow (except P. hrocki, .where it is of 

 moderate breadth). 



a. Eyes subspherical. Rostrum horizontally expanded. 

 Pontoniopsis Borradaile, 1915. 



