714 T. R. R. STEBBING. 



The full definition drawn up by Professor Sars was probably based on the species 

 L. Ugnorum alone. To include the other species undoubtedly belonging to the genus it 

 requires some slight modification. Thus the cpipod of the maxillipeds is not always lanceolate, 

 and the outer ramus of the uropods is not always unguiform. Authors generally (myself 

 included) have agreed in speaking of the trunk limbs as similar in structure, but, while no 

 doubt they have some features in common, especially in regard to the terminal couple of 

 joints, they are at the same time uncommonly well provided with distinguishing points. 

 Between the first gnathopod and the fifth peraeopod the contrast is sufficiently striking. 



The four species now known, all of them small, pale, setose, and very much alike in 

 general appearance, may be distinguished as follows : — 



("Maxillipeds with epipod shorter than the second joint, 



outer ramus of uropods unguiform. 1. L. Ugnorum (J. Rathke), 1799. 



Maxillipeds with epipod longer than the second joint, 

 outer ramus of uropods not unguiform. — 2. 



(Both rami of uropods very small. 2. L. antarctica, Pfefifer, 1887. 



(Only the outer ramus of uropods very small. — 3. 



/Epipod of maxillipeds narrow, mandibular 



J palp diminutive. 3. L. segnis, Chilton, 1883. 



Epipod of maxillipeds broad, mandibular 

 \ palp well developed. 4. L. pfefferi, n. sp. 



In the well-known species of the Atlantic coast Harger notices that in the mandibles 

 ' below there is a slight tubercle, appai-ently the rudiment of the molar process.' His con- 

 jecture is supported by the rather stronger development of this tubercle in L. segnis. 

 Between the acutely lanceolate epipod of the L. Ugnorum, and the forms with rounded apex 

 in L. segnis and L. pfefferi, the narrow leaf shape in L. antarctica offers an intermediate 

 term. In his elaborate description of the last-named species Dr Pfefifer broaches an extra- 

 ordinary theory that ' the pleopods in general have not the value of a limb but of an epipod, 

 so that accordingly the branchial plates of the Isopoda Like those of the Decapoda are 

 epipods, and therefore in a certain sense equivalent formations.' That this view has met vrith 

 no acceptance was to be expected. 



11. Limnoria pfefferi, n. sp. PI. LII A. 



The general appearance in close agreement with L. Ugnorum, like which it has the head 

 almost globular, much narrower than the rest of the body, the first segment of the peraeon 

 much the longest with a conspicuous dorsal V-shaped grooving, the side-plates of the second 

 and third segnaents quadrangular oval, the four following pairs more or less acute, the upper 

 surface of the body beset with hairs of varying length. In the pleon the angles of the 

 first segment are a little less prominent than those of the four following segments; the fifth 

 at the middle is as long as the first four together, and about half as long as the almost 

 circular, flatly saucer-shaped telsonic segment, mth the proximal part of which it shares in 

 forming a smoothly rounded median elevation. 



The eyes are wide apart, very small. 



The first antennae have the second joint subequal to the third, not shorter as in 

 L. segnis and L. Ugnorum, and the second joint of the flagellum is not so abruptly narrower 



