SYSTEMATIC ACCOUNT 175 



Pseudidothea bonnieri Ohlin, 1901 (Text-fig. 14a-/) 



P. boimeiri, Ohlin, 1901, pp. 276-81, pis. .xx and xxi, fig. 6; Barnard, 1920, pp. 380-1; Nordenstam, 1933, p. 114, 

 fig. 27. 



Occurrence. St. WS 212: 30. v. 28, 49° 22' 00" S., 60" 10' 00" W., 242-249 m., i ? (non-breeding). St. WS 214: 

 31. V. 28, 48' 25' S., 60" 40' W., 208-219 m., I o". St. WS 756: 10. X. 31, from 50 53' S., 60 00' W., to 50' 56-3' S., 

 59° 56' W., 117 m., 2}$ (non-breeding), 2 immature. St. WS 766: 18-19. x. 31., 44" 58' 00" S., 60' 05-5' W., 

 545 m., 2 SS and 4 immature. St WS 818: 17. i. 32., 52° 30-5' S., 63° 27' W., 272 m., from Cidaroid spines, 3 im- 

 mature specimens. St. WS 825: 28-29. '• 32. 50° 50' S., 57° 13' W., 135 m., from Cidaroid spines, 6 $$ (breeding), 

 3 SS> 8 immature. St. WS 839: 5. ii. 32, 53° 29-5' S., 63' 31' W., 503 m., from Cidaroid spines, 5 2$ (breeding), 

 6 (JJ, and a number immature. St. WS 871 : i. iv. 32, 53° 16' S., 64' 12' W., 336-341 m., i ^, i immature. 



Remarks. The largest specimen in the Discovery collections is a female in the breeding condition, 

 12 mm. in length and 4 mm. in greatest breadth; the largest male is 9-5 mm. in length and 3 mm. in 

 breadth; the length is the same as that given by Ohlin (1901, p. 281) for the type specimen. My 

 observations on this species differ from those of Ohlin (1901) in the following details: 



The antennule (Text-fig. 14c) consists of a peduncle of three joints, the second one of which bears 

 on its outer side a rounded tubercle, the apex of which is armed with four short spinules. The flagellum 

 consists of two joints (Text-fig. 12b), the first one of which is extremely short. This joint was over- 

 looked by Ohlin. The terminal joint is fairly broad, with a rounded extremity bearing eight sensory 

 setae. 



According to Ohlin, the first and second joints of the antennular peduncle are coalescent, so that 

 there is no articulation between them, the suture being visible only from below or en profile. Norden- 

 stam (1933, p. 113) said that the peduncle is better described as consisting of five joints, and continues: 

 'the short proximal joint is indistinctly marked off on the ventral side from the second'. My own 

 observation on this point agrees with Nordenstam as far as the number of joints is concerned, but the 

 proximal one is not ' indistinctly marked off on the ventral side from the second ', but is a distinct joint 

 (Text-fig. i4«). A tubercle, very similar to that found on the second peduncular joint of the antennule, 

 is present on the second peduncular joint of the antenna. The flagellum consists of two joints with a 

 distal spine which may be regarded as the rudiment of a third, terminal joint. 



The details of the cutting edges of the mandible require some amplification. The primary cutting 

 edge of the left mandible (Text-fig. 14c) bears four teeth; the secondary one bears three teeth, and 

 between this and the molar tubercle are four spines ; the molar tubercle is large, triangular truncated, 

 with a denticulate margin. The primary cutting edge of the right mandible (Text-fig. i\d) bears three 

 teeth, the secondary one is more delicate and less chitinized than the corresponding one on the left 

 mandible; it bears six teeth. The molar tubercle is very similar to that of the left side. 



The marsupium of the breeding female consists of four pairs of brood lamellae formed on the 

 coxae of the second, third, fourth and fifth pairs of thoracic appendages ; the first pair of these is of 

 the usual isopod type, that is, it is folded and the smaller anterior lobe covers the mouthparts; the 

 larger, posterior lobe forms the anterior boundary to the brood chamber. The maxilliped of the 

 breeding female bears a coxal lobe. The ventral integument in the region of the marsupium is soft 

 and unchitinized (cf. the introduction to the suborder Valvifera, pp. 147-148). 



The form of the penial process in the male of this species has already been dealt with in the intro- 

 duction to this suborder (see p. 149 and Text-fig. i^). 



Distribution. The species is restricted to an area around the Falkland Islands. Ohlin's specimens 

 were taken in 43° 6' S., long. 60" W.; Nordenstam's specimens were collected south of West Falkland 

 Islands, and those of the Discovery collections were caught between 45° 13' S., 59" 56' 30" W. and 



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