exotic Sessile-eyed Crustaceans. 187 



dered together. The second division is nearly three times as 

 long as tlie first, and for two thirds of its length is nuicli in- 

 flated; it tiien becomes slightly constricted and considerably 

 depressed. Of the caudal appendages the outer plate is much 

 smaller than the inner both in length and breadth, and is oval 

 in shape. The inner plate follows much the same curve along 

 its free border ; but, where it closely adjoins the tail-segment 

 to which it is united, it has a slight concavity fitting the corre- 

 sponding convexity of the tail-piece. On the underside of 

 the animal a broad fold of this last tail-segment stretches the 

 whole length of each side of it ; beneath the narrower part 

 of the segment the edges of these folds meet. 



There is a species of Sp/ueroma [Sj)h(erovia Jurinii) described 

 by Milne-Edwards from the Egyptian crustaceans of Savigny 

 and Audouin, of which he says : — " This species appears to be 

 very near to Sphceroma serratum, but is distinguished from it 

 by the form of the last segment of the abdomen, which is pro- 

 longed backwards into an obtuse point. The external plate 

 of the caudal appendages has its edge smooth. The length 

 is about two lines." This, as far as it goes, might fairly suit 

 the present species ; but as nothing is said of the great dif- 

 ference in size between the plates of the caudal appendages, 

 which are in consequence very unlike those of Spheroma ser- 

 ratuiiij there can be little doubt that the present is a distinct 

 species, for which I propose the name of Sphceroma algoense. 



It is scarcely of importance to mention that both this and 

 Seha Saundersii are light yellow in colour, since the colour 

 may have faded or changed since the animals' deaths. It 

 may be remarked, too, that some of our English species of 

 Sphceroma are exceedingly variable in colour. , 



IV. Before closing this paper, I may observe that along 

 with the new species some very small specimens have pre- 

 sented themselves of Arcturus lineatus, described and figured 

 in the 'x\nnals'for August 1873, above referred to. The 

 point demanding notice in reference to these young specimens 

 is that the fourth segment of the thorax is not elongated as 

 in adult life — a point the more interesting, because upon this 

 character Milne-Edwards grounds a division of the genus Arc- 

 turns into two sections : — one containing the large Arcturus 

 Baffini from Baffin's Bay, which has the segment in question 

 not elongate ; the other containing the British ^/-c^MrMs lonrji- 

 cornisj which has this one segment as long as all the otlier 

 body-segments put together. Of these sections Goodsir made 

 a genus Arcturus and a genus Leachia — a division obviously 

 now inconvenient, since according to it our Arcturus lineatus 



