Mr. C. Spence Bate on the British Diastylidae. 461 



equalling about half the length of the entire animal. The third 

 thoracic leg, the homologue of the claw in the Decapods, is very 

 long, reaching to the anterior margin of the carapace ; the four 

 succeeding are much shorter, being scarcely longer than the 

 basal joint of the preceding. None of them appear to be 

 furnished with apalpe. 



The abdomen is well developed, and partakes of the character 

 of the higher types in the way in which the lateral edges overlap 

 the sides and seem to protect the delicate appendages beneath, 

 which consist, to each segment, of a pair of organs formed each 

 of a basal joint and a pair of flexible scale-like appendages. 



The appendages of the sixth or penultimate segment resemble 

 those of the preceding species. The telson is rudimentary. 



This very elegant species was taken in the Moray Frith by the 

 Rev. Geo. Gordon, among several specimens of Halia trispinosa. 



Having examined all the forms of the family that I have met 

 with, or believe to have been discovered as British, and the struc- 

 ture of those of which I could obtain more than a single specimen, 

 it will be necessary that I should compare them with the larvae 

 of the Decapoda Macroura, since Agassiz^ assertion that he has 

 taken CumcB from Hipj)olytey &c., is so very positive. All the 

 species mentioned by Agassiz are American — it will therefore 

 be difficult for persons on this side of the Atlantic to procure 

 their evidence from the same; but I think an examination of 

 one of the same genus will be quite sufficient, particularly as all 

 the Diastylidce that have been examined in this paper are British ; 

 consequently, if they are the young of any of the Decapoda 

 Macroura, as asserted by Agassiz, they must be those of British 

 forms. The larva which I have chosen as being the nearest to 

 those mentioned in Dana^s work, is that of Hippolyte varians, 

 of which I have given a careful figure in PI. XV. fig. viii. It 

 was obtained direct from the parent, — therefore in the same 

 manner that Agassiz obtained his Cumce. 



The carapace, furnished with a distinct rostrum, is broad, and 

 not laterally compressed ; it reaches back to the commencement 

 of the abdomen, which consists of but three segments, the ter- 

 minal one being dilated at the extremity into a fish-tail form, 

 having seven unequal spines on each division. 



The eyes are large, situated laterally at the anterior portion of 

 the carapace, and extend on each side beyond the margin ; they 

 can scarcely be ranked among the sessile forms of the organ, as 

 typified among the Edriophthalma. 



The anterior antenna (PL XV. fig. 2) has at least two segments 

 to the peduncle, and two terminal short filaments (the number 

 belonging to the genus in the adult form). The posterior 

 antenna (PI. XV. tig. 3) consists of a peduncle with two seg- 



