360 THE PLANKTON OF THE FAROE CHANNEL AND SHETLANDS. 



Challengeron balfouri {? var), J. Murray, 

 Plate II., Figs. 2 and 2a. 



Shell rather broader than long towards the base, compressed laterally, 

 of the usual diatomaceous structure. At the aboral margin are two 

 short conical teeth — one on the ventral, the other on the dorsal aspect. 

 The peristome is deeply cleft ventrally, and strongly keel-shaped dorsally. 

 It is bifid at the apex, with one tooth rather shorter than the other. 

 The peristome is marked with transverse ridges (not the diatomaceous 

 shell structure), especially in the cleft of the ventral side and along 

 the external surface of the peristome and edge of the teeth. The 

 mouth is wide, and has no pharynx. 



Length of the shell, "2 mm.; breadth, '212 mm,; length of the 

 peristome, "093 mm. ; length of the aboral spines, "03 mm. ; width of 

 the mouth, '05 mm. 



Challengeron balfouri, variety. Plate II., Figs. 3 and 3a. 



This species resembles the preceding, except in the characters of the 

 peristome, which is stouter and posteriorly produced into a rather 

 prominent elbow, above which the peristome ends in two pointed 

 divergent teeth. The peristome is strongly marked with ridge mark- 

 ings, but not on the elbow, and on the ventral aspect in the groove. 

 It is essentially tlie same, except in the characters of the peristome, as 

 the last species. It was taken at 350 fathoms along with the last 

 species. 



Neither of these two species exactly corresponds with Haeckel's 

 description of C. lalfouri {Challenger Report, " Eadiolaria," p. 1655), 

 which was a surface species. Both the examples described are probably 

 deep-water varieties of G. balfouri. 



Challengeria tritonis {Haechel). Plate II., Fig. 4. 



The shell is longer than broad, ovate seen from the dorso-ventral 

 aspect, marked apparently diatomaceously ; but this is not of the usual 

 aspect, but consists of simple rounded pits, many of large size, and 

 the usual hexagonal framework between the pits is absent in this case. 



The mouth is comparatively small, and forms a rounded opening, 

 situated rather on tlie ventral aspect of the shell. There is a long 

 peristome tapering to a blunt point, directed vertically, and having fine 

 markings on the dorsal and ventral sides, unbranched and possessing 

 no teeth. 



Length of the body of the shell, "2 mm. ; of the peristome, '1 mm. ; 

 width of the body of the shell, '17 mm. ; width of the mouth, '04 mm. 



