44 ISOPODA. 



CYMODOCE TRUNCATA (Montagu), Leach. (PI. IV. figs. 3-14.) 



1868. Cymodocea truncata (Montagu), B. & W. vol. ii. p. 426, rf . 



1868. Cymodocea emarginata (Leach), B. & W. vol. ii. p. 428, J . 



1868. Sphceroma curtum (Leach), B. & W. vol. ii. p. 412, $. 



Ib68. Sjjh(eroia Prideauxianum, Leach, B. & W. vol. ii. p. 415, 2 



We have examined the types of the four above so-called 

 species in the British Museum, and are satisfied that they all 

 belong to the two sexes of one species. As long ago as 1884 

 we took the two sexes in coitu at Falmouth. The type 

 specimen of C. emarginata differs from that of C. truncata in 

 having the segments of the metasome covered with somewhat 

 larger granulations than usual ; but selecting a somewhat 

 similar specimen from among C. truncata, and then rubbing 

 off all setn 1 , C. emarginata was imitated (fig. 4). But B. & 

 W.'s fig. "p," on page 428, does not correctly represent the 

 central process of the last segment as seen from below, for it 

 is nearly parallel-sided, and not ovate as drawn. There is con- 

 siderable variation in the development of the tubercles on the 

 metastome of the female, which are now well elevated and 

 nearly round; now much less conspicuous and more elongated; 

 now almost obsolete. 



In the British Museum, among many examples of the 

 species procured by the late Mr. McAndrew at Shetland, are 

 two small specimens which differ from all others which we 

 have seen. They are only 5'5 mm. long. The last segment 

 of the metasome, or telson (fig. 6), has two greatly elevated 

 ridges which slightly converge behind, and show a faintly 

 indicated longitudinal hollow. These ridges are much more 

 developed in proportion to the size of the entire animal than 

 we have seen in any female specimens, and they possibly 

 represent, the young stage of the male. 



The mouth-organs of the female present two entirely 

 different types. In the largest specimens examined they are 

 as figs. 7, 8, 9, 10, and resemble the same parts in the male 

 of Cymodoce, but differ from those of the genus Sphwroma in 

 several particulars, but chiefly in the forms of the mandibles 

 and maxillipeds ; these large specimens did not contain any 

 embryos. The second form of the mouth-organs was found 

 in examples which in size were rather more than half-grown. 

 In these specimens the whole of the interior of the body was 

 crammed with embryos, which filled every part, even the 

 mouth itself, so that it seemed impossible that the animal 

 could swallow any solid substance. Here the mouth-organs 

 were very greatly modified, so as to assume a much more rudi- 

 mentary character. A comparison of figs. 11, 12, 13, 14 with 

 figs. 7-10 will show that in the mandibles the masticatory 



