CRUSTACEA. 307 



eyes, are but little produced and rounded, and are received into 

 rounded notches in the first segment of the body. The first body- 

 segment is longer than the following ; its antero-lateral processes 

 narrow, acute, and prolonged forward along the sides of the head 

 beyond the eyes ; the postero-lateral angles of all the segments 

 (the last excepted) are acute, those of the last body-segment are 

 rounded. The postabdomen is divided into two portions, the ante- 

 rior of which is minutely punctulated and bears on each side two 

 lateral sutures, indicative of coalescent segments ; the posterior 

 (or terminal segment) is granulated, sub triangulate, with two low 

 rounded elevations on its upper surface ; its distal extremity has a 

 rather deep and narrow and somewhat triangulate notch. The 

 basal joint of the peduncle of the antennules is much enlarged, 

 longer than broad, its distal extremity is excavated, and its distal 

 and inferior angle is prolonged into a spine which reaches nearly to 

 the extremity of the following joint, which is also dilated, but 

 shorter than the preceding ; the very slender flagellum is .12-14- 

 jointed ; the four exposed joints of the peduncle of the antennae are 

 slender, but little more dilated than the joints of the flagellum, 

 which are 14-16 in number. The fourth to sixth joints of the 

 ambulatory legs are slender and margined with very short hairs. 

 The rami of the uropoda are rather large and dilated, reaching 

 beyond the distal end of the terminal segment, and with the 

 exterior and distal angles acute and somewhat produced (especially 

 in the outer ramus, which is father the larger) . Colour (in spirit) 

 yellowish white, minutely speckled with black. Length nearly 

 6 lines (12 millim.). 



Our specimen differs from Milne-Edwards's diagnosis in its punc- 

 tulated and granulated postabdomen and the narrower notch of the 

 terminal segment ; the first-mentioned is a character which might 

 possibly be overlooked on an examination with a lens of low power ; 

 nevertheless this variety will perhaps prove a distinct species. 



The remarkable structure of the antennules serves, I think, to 

 distinguish it genericaUy from the typical species of Dynamene, 

 which it resembles in the simply emarginate tail-segment ; but it 

 may be found convenient hereafter, to separate genericaUy the 

 species with a tridentate terminal postabdominal segment from 

 those in which this segment is simply, notched, as has been done in 

 the analogous case of Cymodocea ; the examination, however, of 

 further material is required to determine this question. Certain 

 species with a tridentate segment closely connect this genus with 

 Oymodocea. I may take this opportunity of noting that the Cymo- 

 docea gramdata described by me in 1876* is probably not specifi- 

 cally totinguishable from Gerceis tridentata, Milne-Edwards, which 

 species, however, is but very briefly characterized. 



* Vide 'Catalogue New-Zealand Crustacea,' p. 114, pi. iii. fig. 5 (1876). 



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