1900.] FBOil THE FALKLAND ISLANDS. 559 



compose it the general form of the body, prolonged on each side 

 much over the feet, resembles that of the insects known as 

 Cassides, or rather a regularly oval and very inflated buckler. 

 The species that have been successively assigned to the genus are 

 Cassidina typa M.-Edwards, 1840, 0. emarginata Guerin-Meneville, 

 1843, G. latistylis Dana, 1853, C. maculata Studer, 1884, and 

 C. neo-zealanica Thomson, 1888. Of these five, typa and latistylis 

 are under the double disadvantage that their place of origin is un- 

 known and their colour undescribed ; metadata, from Betsy Cove, 

 Kerguelen Island, is described as black-brown with whitish flecks 

 on both sides of the middle line ; neo-zealanica, from the Bay of 

 Islands, New Zealand, has the colour brownish-grey, covered with 

 black spots and star-like markings ; emarginata is reported from 

 the Falkland Islands by Guerin-Meneville, from the Strait of 

 Magellan and the west coast of Patagonia by Cunningham, from 

 the same Strait and Punta Arenas by Studer, from Kerguelen 

 Island by Miers, and from South Georgia by Pfeffer, the last- 

 named writer describing the colour as a quite clear brown mixed 

 with a little green-grey, the whole dorsal surface overspread 

 with minute close-set points, which on the side-plates are some- 

 what larger and closer together. This species attains a length of 

 35 mm., while for the other four the length recorded ranges froni 

 8 to 14 mm. But Studer and Pfeffer are no doubt right in 

 accepting the opinion of Miers that the largest of the four, 

 0. latistylis Dana, is only a junior form of 0. emarginata. 



The question next arises whether C. emarginata itself is distinct 

 from all the other forms. C. typa is described as 4 lines long, 

 thus very little exceeding in length the C. neo-zealanica, to which 

 Thomson assigns " length 8 mm. ; breadth 5 mm." It has been 

 already stated that the colour of 0. typa is not described ; but in 

 the Atlas to the * Histoire Naturelle des Crusfaces ' there is a 

 coloured figure of it, and the uniform light tint of this is out of 

 agreement with any described colouring -within the genus, except 

 that of C. emarginata. It is rather curious, too, that the oval 

 contour of this figure is very suggestive of a large, slightly bent 

 specimen of C. emarginata. As opposed to any suspicions, how- 

 ever, that might arise of an identity between the two species, 

 Guerin-Meneville points out that in his C. emarginata the body 

 is moderately, not greatly, inflated ; the head scarcely broader 

 than long, while in Milne-Edwards's figure the head is very broad 

 and very short with the eyes situated at a great distance one 

 from the other ; the last segment of the pleon triangular, truncate 

 and a little emarginate at the apex, instead of having the apex 

 narrowly rounded ; the first antennae reach a good deal, instead 

 of scarcely at all, beyond the peduncle of the second ; the fourth 

 and fifth limbs of the peraeon have the basal joint strongly 

 bent, instead of straight ; and the uropods have the inner lobe 

 very broad, reaching clearly beyond the telson, with the distal 

 margin obliquely truncate and a little emarginate, whereas in ODe 



37* 



