REPORT ON THE ISOPODA. 11 



tluit I was able to examine the iuuer edg'e of the mandibles is strongly toothed. Schiijdte, 

 in a memoir upon the structure of the mouth in the Isopoda,^ has figured and described 

 the mouth parts of Serolis paradoxa ; the mandibles are distinguished from those of other 

 Isopoda by their blunt edge, wliieh renders them especially fitted for grinding and not for 

 tearing, and Schiodte suggests that the food of Serolis jirobably consists of " such animals as 

 have firm integuments ; " in all the specimens that I have examined the stomach contained 

 debris of other Crustacea, frequently recognisable fragments of their own species, besides 

 Diatoms, morsels of the calcareous structure of Echinodermata, &c. ; Schiodte is therefore 

 quite right in his supposition regarding the food of Serolis, and is no doubt justified in 

 distinguishing this genus from other Isopoda by the characters of its mouth appendages. 



The mandibles of Serolis, however, possess additional cutting blades and spiniform 

 processes which appear to have been overlooked or imperfectly described and figured liy 

 all previous writers with the exception of Schiodte. On PI. II. figs. 2, 3 are figured the 

 distal extremity of both mandibles right and left of Serolis latifrons; the left mandible 

 has upon the upper surface a triangular chisel-like blade, and below this a long spine ; 

 the right mandible has the spine, but the cutting 1;)lade is smaller. The left mandible 

 of other sj)ecies is quite similar to that of Serolis latifrons, but as a general rule 

 {cf. e.g., fig. of Serolis schythei, PL II. figs. 12, 13) the cutting blade is not present on the 

 right mandible, its place being occupied by a large spine-like structure. The presence 

 of these structures appears to me to fit the mandibles for tearing as well as grinding. 



The asymmetry of the mandibles is marked not only by the differences just mentioned 

 l)ut also by the general shape of the masticatory edge {cf. e.g., PI. II. figs. 12, 13) and by 

 the fact that one mandible, generally the left, is smaller than the other. An asymmetry 

 (jf the mandibles appears to be a fairly constant character of the Isopoda. 



The riiaxillce are small and delicate ; the anterior pair consist of a narrow basal 

 portion or " cardo," with which is articulated a long flat somewhat curved distal lobe ; the 

 free edge of this is furnished with a considerable number of strong spines dark yellow in 

 colour. In some species (e.g., Serolis 'pallida) the lobe of the maxilla is much more bent 

 upon itself and proportionately shorter. In many species I have observed an additional 

 lobe, which is situated below the large masticatory lamina articulating with the cardo 

 (see. PI. V. fig. 14); the presence of this was noticed by Audouin and Milne-Edwards, 

 but subsequently denied by Grube." 



The second pair of maxillaj are smaller and more delicate than the anterior jiair, but 

 like them consist of a basal portion or " cardo "' and a distal portion, which is divided into 

 two lobes, the upper of which is again suljdivided ; the two anterior are subequal and 

 smaller than the posterior lobe, which is separated by a distinct suture ; the free 

 extremities of all bear a number of hairs more delicate than those on the first maxilla', 



1 KriPyer, Nat. Hist. TichsJci:, ser. 3, vol. iv. (ISdO) ; translated in A nn. mtd Mag. Nat. HUt., ser. 4, vol. i. p. 1 ct setp 

 - Archivf. Naturgese.h ., Jalirg. xli. Bd. i. p. 214. 



