2^ 



Polychelus nanus (Smith). 



Pentacheles nanus, Smith, 1884. 

 Pentacheles nanus, Smith, 1886. 

 Polycheles nanus, Faxon, 1895. 

 Polycheles nanus, Caulleiy, 1896. 

 Polycheles nanus, St ebbing, 1908. 

 Polycheles nanus, Hansen, 1908. 



P. nanus, var. Grimaldii, Bouvier. 



PL I, figs. 14-15. 



Polycheles Grimaldii, Bouvier, 1905 (b). 



This species is closely allied to P. sculptus and both Faxon and 

 Smith suggest that it may be merely a dwarf deep water variety 

 of that species. It seems, however, to be distinguished by well- 

 marked characters, which Smith, who has examined a large 

 number of specimens, says are very constant. Hansen has also 

 seen a large amount of material and is convinced that it 

 forms a species quite distinct from P. sculptus. 



The various spines and grooves are more robustly developed 

 than in the last species. The sides of the carapace are slightly 

 convex ; the spines on the lateral margin are very slender and 

 project almost at right angles ; there are five or six in front, 

 three in the central part, and seven behind. The frontal margin 

 is concave considered as a whole, and is divided into three parts 

 by the deep orbital sinuses. These are rounded posteriorly and 

 do not narrow to a fine point as in P. typhlops. At the inner 

 angle of each orbital sinus there is a small spine on the median 

 lobe of the cara23ace in P. Grimaldii as described by Bouvier. 

 As this, however, is the only difference between it and P. nanus, 

 1 have thought it best to give it merely the rank of a variety. 

 Sometimes there is a blunt spine or process below the rostrum, 

 but it is not so large as in P. typhlops, and is not a constant char- 

 acter. The rostrum is formed of two small spines. The median 

 carina has its spines arranged as follows: — R + 1, 1, 2, 1; 

 2, 2, 2. The hind margin of the carapace has two small spines 

 on each side beside the median ones. The carina which lies 

 between the median line and the lateral margin has ^ve prom- 

 inent spines interspersed with smaller ones, and curves slightly 

 inwards. The oblique line running outwards and forwards 

 from the poster or cardiac region is well-marked and sp ny. 

 The submarginal carinae are well developed and furnished with 

 distinct teeth. 



The median carinal spines on the abdominal segments are 

 longer and more strongly curved than in P. sculptus. The first 

 segment, which is much narrower than the others, has two teeth 

 on the lateral part of the tergum, one above and one below the 

 point of attachment to the hind margin of the carapace ; the 

 carinal spine is not greatly developed. On the second segment 

 the carinal spine is still quite low. In the next three segments, 

 however, the median spines reach an enormous size and project 



