Report on the zoological collections made in the Indo-Pacific Ocean ...

;CETISTACEA. 307eyes, are but little produced and rounded, and are received intorounded notches in the first segment of the body. The first bodysegmentis longer than the following ; its antero-lateral processesnarrow, acute, and prolonged forward along the sides of the headbeyond the eyes ; the postero-lateral angles of all the segments(the last excepted) are acute, those of the last body-segment arerounded. The postabdomen is divided into two portions, the anteriorof which is minutely punctulated and bears on each side twolateral sutures, indicative of coalescent segments ; the posterior(or terminal segment) is granulated, subtriangulate, with two lowrounded elevations on its upper surface ; its distal extremity has arather deep and narrow and somewhat triangulate notch. Thebasal joint of the peduncle of the autennules is much enlarged,longer than broad, its distal extremity is excavated, and its distaland inferior angle is prolonged into a spine which reaches nearly tothe extremity of the following joint, which is also dilated, butshorter than the preceding ; the very slender flagellum is 12-14-jointed ; the four exposed joints of the peduncle of the antennae areslender, but little more dilated than the joints of the flagellum,which are 14-16 in number. The fourth to sixth joints of theambulatory legs are slender and margined with very short hairs.The rami of the uropoda are rather large and dilated, reachingbeyond the distal end of the terminal segment, and with theexterior and distal angles acute and somewhat produced (especiallyin the outer ramus, w^hich is rather the larger) , Colour (in spirit)yellowish white, minutely speckled with black. Length nearly6 lines (12 millim.).Our specimen differs from Milne-Edwards's diagnosis in its punctulatedand granulated postabdomen and the narrower notch of theterminal segment ; the first-mentioned is a character which mightpossibly be overlooked on an examination with a lens of low powernevertheless this variety will perhaps prove a distinct species.The remarkable structure of the antennules serves, I think, todistinguish it generically from the typical species of Dynamene,which it resembles in the simply emarginate tail-segment ; but itmay be found convenient hereafter to separate generically thespecies with a tridentate terminal postabdominal segment fromthose in which this segment is simply notched, as has been done inthe analogous case of Cymodocea ; the examination, however, offurther material is required to determine this question. Certainspecies with a tridentate segment closely connect this genus withCymodocea. I may take this opportunity of noting that the Cymodoceagranuhta described by me in 1876* is probably not specificallydistinguishable from Cerceis trich'ntata, Milne-Edwards, whichspecies, however, is but very briefly characterized.* Vide 'Catalogue New-Zealand Crustacea,' p. 114, pi. iii. fig, 5 (1876).x2