276 DISCOVERY REPORTS 



thoracic appendage of the aduh male of S. exigua, Nordenstam. These are not found 

 in the corresponding position in the female. 



The so-called "frontal sense organ" first described by Grube (1875, p. 225) in his 

 account of S. paradoxa, Fabricius, appears as an oval semi-transparent area on either 

 side of the head on the lateral part of the cephalosome. Beddard {I'&^^b, p. 17) states 

 that such a structure is present in many species of Serolis, and in a footnote further 

 remarks that it generally has the form of a deep and narrow groove surrounded by a 

 specially thickened rim, and that in S. schythei, Lutken, and S. cornuta, Studer, there 

 is a pore on the under-surface of the epimeron exactly beneath it. 



There is no doubt that such an area does appear in many species of Serolis, but I have 

 failed to find the " thickened rim " surrounding a deep and narrow groove, or the " pore " 

 on the under-surface. After the careful examination of a number of specimens of 

 several species I have come to the conclusion that this area simply represents a certain 

 thinness of the ventral chitinous coat brought about by the rubbing movement of the 

 distal end of the propodus of the second thoracic appendage, which Ues in this position 

 when the appendage is not extended, and that it has no connection with any sensory 



fvmction. 



The oostegites appear in one of two forms: in the non-breeding female as chitinous, 

 parallel-sided plates which reach the middle of the segment and are found on the 

 second to the fifth thoracic somites ; and in the breeding female as four pairs of large 

 lamellae overlapping to form a complete marsupium. This overlapping alternates in 

 successive segments: in the first and third somites the left lamella overlaps the right, 

 and in the second and fourth the right overlaps the left. In no case do my observations 

 agree with those of Studer (1879), who states that the lamellae of the right generally 

 cover those of the left side. 



It is interesting to note that in this family the form of the first pair of oostegites (Fig. 2 /) 

 is similarly modified to that of Asellus aquatiais and of the members of the family 

 Phreatoicidae. Each consists of a main posterior portion {A) which form the anterior 

 boundary of the marsupium, and a smaller anterior portion {B) which envelops the 

 base of the maxilliped of its own side. When viewed from below these two parts are seen 

 to be separated from each other by a groove, at the bottom of which is a non-chitinous 

 strip (C), this latter appearing to act as a hinge between the two parts of the lamella. 

 It seems probable that, as in Aselliis aquaticus and the Phreatoicidae (Sheppard, 1927, 

 p. 91), the anterior parts of these lamellae, together with the coxal lobes of the maxil- 

 lipeds, form an additional aerating apparatus for the marsupium. 



In giving an account of the sexual characters of the Serolids, Beddard (18446, pp. 14, 

 15) states that when the brood lamellae of the female are fully developed "the sterna 

 of the thoracic segments undergo a retrograde development and almost disappear ", and 

 that "the young appear to be actually contained within the body of the mother, the 

 alimentary canal is pressed up against the dorsal surface of the body, and its cavity is 

 reduced to a minimum". 



With regard to the first part of this statement, it seems more correct to say that, 



