556 REV. 1. R. R. STEBBING ON CRUSTACEANS [May 22, 



reminds us that the young of Porcellio have at first only six peraeon- 

 segments and six pairs of legs.' It is rather provoking that he 

 did not give fuller details, since in his account so far as it goes 

 there are many points calculated to excite some surprise. The 

 small size, the linear foriu, the anal filament, the heart-shaped 

 caudal segment with uropods projecting to the rear, were little 

 to be expected in the young of Sphceroma gigas. The truth 

 appears to me to be that Guerin-Meoeville was misled by the 

 minute size and semi-pellucid hue of lais pubescens (Dana) into 

 supposing it to be the young of the Sphceroma, of which it is, so 

 far as known, the invariable companion. 



We now pass to the description of the adult ExospJiceroma gigas. 



The short but broad vertex of the head is separated from the 

 occiput by a nearly straight ridge, the front line of the vertex 

 being indentured on either side of a short rostral point, its outer 

 angles meeting the advanced points of the sides of the first peraeon- 

 segment a little in front of the eyes. All the segments of the 

 peraeon have the grooving described by Miers. The segments 

 from the second to the seventh are almost parallel-sided, but the 

 sixth and seventh slightly widen out. Again, the first division 

 of the pleon is infinitesimally wider than the seventh segment 

 of the perseon. This first part of the pleon is composite, a 

 continuous line near the base, and for the most part usually 

 concealed under the peraeon, marking off the first segment, while 

 from the broad second, the successively narrower third and fourth 

 are marked off by lines which ai'e interruptt^d at some distance 

 from the middle. The second division probably consists of an 

 obscure and concealed fifth segment, the sixth carrying the 

 uropods and the telson. This division is so adjusted that in 

 spirit-specimens the animal cannot be flattened out but has a 

 crook in its back, which would appear to facilitate a doubling 

 together of the body rather than the spherical form so readily 

 assumed by Spha^roma serratum. The inflation of the caudal 

 shield declines rather rapidly near the slightly sinuous sides and 

 the rather narrow rounded apex. 



The eyes are dark, small, irregularly oval, near the postero- 

 lateral corners of the head. 



First antennae. — First joint large, broad, with basal fold, second 

 much smaller, third longer but much narrower than second ; 

 flagellum shorter than peduncle, 17-jointed, each joint except first 

 and last carrying two hyaline filaments. 



Second antennae. — Longer than first, with stouter flagellum of 

 about 16 short and stout joints. 



Epistome widening much downward. Upper lip with distal 

 margin almost straight, except at the angles. 



Mandibles. — Cutting-edge tridentate, accessory plate stronger 



* M. Louis Roule, " Etudes sur le Developpement des Criistaces," Ann. Sci. 

 Nat. ser. 7, vol. xviii. pp. 46, 57, 64 (1895), contravenes tliis long-accepted 

 statement, though admitting the small comparative size of the seventh segment 

 and its pair of appendages. 



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