558 BET. T. R. E. STEBBING OS CBUSTACEAK8 [May 22, 



the subacute apex ; the uropods have their apices subacute, that 

 of the outer ramus the sharper and turned slightly outward. It 

 is light coloured, with two transverse narrow dark bands. This 

 specimen ought perhaps to be called Exosphceroma lanceolatum 

 (White) ; but one has to remark that Leach describes his species 

 as having the " last segment of pleon narrowed to a point," so 

 that the original gigas may have been the lauceolate form. Dana 

 speaks of the lamellae of the uropods in lanceolatum as " lanceolate, 

 obtuse ; " and if other distinctions are not more steadfast than 

 those based on the apices of the tel^on and uropods appear to be, 

 the two names gigas and lanceolatum may well stand in one 

 synonymy. 



Colour. In formol. the specimens are dark or light brown, the 

 rows of whitish markings on the peraeon being more conspicuous 

 in dark than in light-coloured examples; the whole body is covered 

 with minute blackish specks, the head and the peraeon-segments, 

 however, and parts of the pleon, having clear borders which are 

 sometimes orange in hue. 



Size. Length about 18 mm., breadth 11 mm. 



Mr. Vallentin took this species in Stanley Harbour, where it 

 abounds. He says : " This species is usually to be found during 

 low water under stones ; but during a calm, and especially if the 

 sun is shining brightly, they come to the surface and swim about in 

 an aimless manner, in an inverted position, the paired appendages 

 of the telson standing out at right angles to the body. I frequently 

 caught them swimming in this manner when in my boat, and when 

 so captured they would immediately roll themselves up into a ball. 

 On being replaced in the sea, an individual would sink a few 

 inches, and mounting to the surface swim as vigorously as before. 

 When swimming in this manner these crustaceans would always 

 keep near the shore, where the water is not more than two 

 fathoms in depth." Dr. Coppinger (cf. Miers, 1881) records small 

 specimens from 9-10 fathoms at " Sandy Point." 



Gen. Cassidina Milne-Edwards. 



1840. Cassidina, Milne-Edwards, Hist. Nat. Crust, vol. iii. 

 p. 223. 



1843. Cassidina, Guerin-Meneville, Iconographie du Kegne 

 Animal, Crust., texte, p. 31. 



1853. Cassidina, Dana, IT. S. Expl. Exp. vol. xiii., Crust, p. 748. 



1884. Cassidina, Studer, Isopoden Eeise ' Gazelle,' p. 19. 



1887. Cassidina, Pfeffer, Krebse von Siid-Georgien, p. 20. 



1888. Cassidina, G. M. Thomson, Tr. New Zealand Inst, 

 vol. xxi. p. 263. 



1900. Cassidena, H. Richardson, The American Naturalist, 

 vol. xxxiv. p. 222. 



The origin of the name of this genus is indirectly explained by- 

 Milne-Edwards when he says that in the Sphaeromidae which 



