SPECIES PRESENT IN'THE SAMPLES 265 



The description and figures given by Skogsberg (1920, p. 649) under the name Conchoecia rotundata 

 may be taken as typical for this species. Type material will be deposited at the British Museum. The 

 distribution known at present is in the Antarctic and colder waters of the Atlantic, distribution north- 

 wards possibly being due to the cold Benguela current. In the present series of samples moderate 

 numbers of adults and juveniles occurred at Stations WS 976-8, 986 and 996 mainly at depths below 

 250 m. A single juvenile was in the 500-250 m. sample from Station WS 997. 



The species may be distinguished from other known species of the genus Conchoecia by the shape 

 of the shell coupled with the position of the unsymmetric glands. Confirmatory characters of the male 

 are the number of pairs of spines on the principal seta of the antennule, the form of the clasping organ 

 of the antenna and the frontal organ. 



The new specific name has been chosen in acknowledgement of Skogsberg's realization that more 

 than one species might have been confused under the name C. rotundata. 



Conchoecia teretivalvata n.sp. ('short forms'). 



C. rotundata Miiller, 1894, p. 229; pi. 16, figs. 16, 18-20 (not fig. 17); pi. 8, fig. 33. 



C. rotundata Miiller, 1906, p. 83 part. 



C. rotundata (stage II) Fowler, 1909, p. 273. 



C. rotundata (part) Miiller, 1912, p. 77. 



Diagnostic description. Male. Length 0-8-0-9 mm. Shell (Fig. 2 a) resembling that of C. 

 kyrtophora in profile, but with the shoulder vaults poorly developed and the whole surface smoothly 

 convex as in the case of C. skogsbergi. The posterior dorsal angle is strongly obtuse, the posterior 

 margin being convex and continuing smoothly into the ventral margin. The greatest depth of the shell 

 valves is just posterior to the middle of the length, and the depth decreases sharply anterior to this 

 point. The left unsymmetric gland (Fig. 20) is situated near the base of the rostrum, just posterior to 

 the anterior extremity of the hinge. The right unsymmetric gland (Fig. 2 c) opens level with the margin 

 of the shell near the posterior extremity of the hinge, there being no tubercle. Medial glands are 

 moderately well developed. Striation of the shell is similar in arrangement to that of C. nasotuberculata 

 but very weak and difficult to observe. 



The principal (V) seta of the antennule (Fig. 3 c) has nine or ten pairs of spines arranged in two 

 rows with the spines of each pair level with one another. Each spine is sharply basally directed, parallel 

 to the seta. The more basal spines are slightly longer than the more distal and the three most basal 

 pairs succeed one another at wider intervals than the distal pairs. The proximal setae have a few 

 extremely fine distally directed setules level with the distal spines of the principal seta. 



The endopodite of the antenna closely resembles that of C. skogsbergi (see Skogsberg, 1920, under 

 C. rotundata) but the clasping organs differ. The right clasping organ (Fig. 3 b) is bent at a right-angle 

 and has the apical portion slightly recurved. It has well-marked transverse striae distally. The left 

 clasping organ (Fig. 3 a) is smoothly curved and slightly recurved at the apex. The apical transverse 

 striae are indistinct. 



The dorsal boundary of the capitulum of the frontal organ (Fig. 2d) is slightly and smoothly 

 concave. Basally it is considerably swollen, which portion bears a few conspicuous ventral spines. 



Female. Length about 0-9 mm. The shell (Fig. 2/) resembles that of the male in general features 

 though it has a greater depth in proportion to its length. It lacks the well-marked shoulder vaults and 

 posterior tubercle, which are present in the similar species, C. kyrtophora and C. nasotuberculata. 



The frontal organ (Fig. ze) has a capitulum with a length slightly more than four times the breadth, 

 and slightly tapering anterior to the middle of its length. The apex is rounded and the whole ventral 

 margin bears short fine spines. 



