354 Transactions. 



Art. XXXIII. — A New Species of Orchestia 



By Charles Chilton, M.A., D.Sc, LL.D., M.B., CM., F.L.S., C M.ZS., 

 Professor of Biology, Canterbury College, New Zealand. 



{Read before the Philosophical Institute of Canterbury, 3rd November, 1915.] 



Of the numerous species of Orchestia that are found on the coasts of New 

 Zealand one of the commonest is Orchestia chiliensis Milne-Edwards, usually 

 found under stones, seaweed, &c., on rock}' shores, but not on sandy beaches. 

 In general characters it resembles 0. mediterranea A. Costa, of Europe, and 

 it agrees well with the short description given by Stebbing in " Das Tierreich 

 Amphipoda," p. 537. The species can usually be recognized ia the fully 

 developed male by the stout peduncle of the lower antenna and by the 

 somewhat widened meral and carpal joints of the fourth and fifth peraeo- 

 poda ; the females and immature males are, however, much more difficult 

 to distinguish from those of allied species. 



In August, 1915, I received from Mr. T. B. Smith, of the Stephen 

 Island Lighthouse, to whom I am indebted for many interesting Crustacea, 

 a large number of specimens of an Orchestia which I at first thought to 

 be 0. chiliensis M.-E., one imdoubted male of which was, indeed, present. 

 Among them, however, a few of the largest males had the meral and 

 carpal joints of the last two peraeopoda widened into large flat plates, 

 thus differing markedly from the form usually met with in 0. chiliensis. 

 It is, of course, possible that this is only an extreme development of the 

 tendency shown to a less extent in the ordinary specimens of 0. chiliensis, 

 for it is well known that in several Amphipoda the structures specially 

 modified in the male may in certain individuals be developed to an extent 

 that makes them look quite different from the ordinary form. I have 

 described an example of this in the case of Cerapus fldndersi Stebbing,* 

 and other examples could be quoted. In the present case, however, vmtil 

 the relationship between the Stephen Island form and 0. chiliensis is 

 better known it will be safer to consider the former to be a distinct species, 

 and I am therefore describing it under the name Orchestia miranda sp. nov. 



Orchestia miranda sp. nov. Figs. 1 to 6. 



Specific Diagnosis. — In general resembling 0. chiliensis M.-E., the male 

 differing from the female in the stouter lower antenna, in the gnathopoda, 

 and especially in the enlarged joints of the last two pairs of peraeopoda. 

 In the fourth peraeopod the merus is of normal width proximally but 

 widens distally to fully twice this width, thus forming a triangular plate; 

 the carpus is greatly dilated into a large oblong plate with rounded corners, 

 rather wider than the greatest width of the merus ; the propod is not 

 dilated, but of normal width. The fifth peraeopod is modified in a «irailar 



* Rec. Australian Museum, vol. 2, p. 1, 1892. 



