NO. 26 NEW MYSIDACID CRUSTACEANS TATTERSALL 3 



The characters in question may be briefly reviewed as follows : 



Eyes. — In P. microps the eyes are very small, the cornea being very 

 much shorter than the breadth of the basal joint of the antennular 

 peduncle. In all the other species the eye is large, the cornea considera- 

 bly broader than the basal joint of the antennular peduncle. There 

 seem to be no tangible differences between the sizes of the eye in 

 P. glaher, P. sansoi, and P. macrops. The Atlantic specimens are 

 large-eyed. 



Antenna! scale. — In P. microps and P. sancoi the antennal scale 

 extends for only one-third of its length beyond the distal end of the 

 peduncle of the antennule. In the other described species the scale 

 extends for one-half of its length beyond the distal end of the antennu- 

 lar peduncle. The Atlantic specimens belong to the first group. 



Rostral plate. — In all the species the rostral plate is tridentate with 

 the exception of P. macrops, in which the median tooth is wanting. 

 In P. glaher the rostral plate is semicircular, with the lateral teeth 

 rather far back on the lateral margin. In P. sansoi it is large, with 

 the lateral margins parallel and the whole plate rectangular in form. 

 In P. microps it is large with the lateral margins incurving slightly 

 posteriorly. The Atlantic specimens have the rostral plate more like 

 that of P. glaher than the other two species, but the lateral teeth are 

 more nearly on a level with the median tooth, so that the lateral margins 

 are longer than in P. glaher. 



Telsoii.— In this genus the telson is armed distally with two pairs 

 of large spines, between which is a group of smaller spines in a 

 graded series. Between the distal pair of large spines, at the apex of 

 the telson, is a plate armed with five or six teeth, between which are 

 long feathered setae. Proximal to the large spines on each lateral 

 margin are a number of small spines. The details of the armature 

 of the telson in each of the species may be tabulated as follows : 



Pairs of Spines between Spines proximal 



large spines large spines to large spines 



P. glaher 2 6-7 4 



P. sansoi 2 3 8 



P. microps 2 5 3 



P. macrops 2 4 3 



.A.tlantic spec 2 3 3-4 



It is thus clear that all the established species are very closely allied 

 to one another, but it is equally obvious that the Atlantic specimens are 

 as much entitled to specific rank as any of the species established by 

 Colosi, for the differences from the type are of the same magnitude 

 as in the other species. If the isolated geographical area of the Atlantic 



