OCR Text |
Show 1900.] FROM 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, C. emarginata Guerin-Meneville, 1843, C. 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 unknown and their colour undescribed : maculata, 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, N e w 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 somewhat larger and closer together. This species attains a length of 35 mm., while for the other four the length recorded ranges from 8 to 14 mm. But Studer and Pfeffer are no doubt right in accepting the opinion of Miers that the largest of the four, C. latistylis Dana, is only a junior form of C. 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 G. neo-zealanica, to which Thomson assigns "length 8 m m . ; breadth 5 mm." It has been already stated that the colour of C. typa is not described; but in the Atlas to the ' Histoire Naturelle des Crustaces' 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, however, that might arise of an identity between the two species, Guerin-Meneville points out that in his C. emarginata tbe 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 one |