562 RET. T. E. R. STEBBING ON CRUSTACEANS [May 22, 



middle of the back. But neither does Guerin-Meneville take 

 any notice of the peculiar arrangement of the fore part of the 

 pleon in his accouut of C. emarginata, and even Pfeffer's accurate 

 description is very ill supported by the accompanying dorsal figure 

 of that species. 



It remains to consider the C. neo-zealanica Thomson, which 

 agrees in its dimensions with C. typa, and is perhaps not 

 particularly unlike in colouring — two characters, of which the 

 second has but little importance, and the first, apart from other 

 considerations, no importance at all. While quoting at length 

 from Milne-Edwards's generic accouut of Cassidina, Mr. Thomson 

 unfortunately does not call attention to any characters on which 

 he relies for separating his own species from the typical one ; 

 and his specific description would, I think, justify an identification of 

 one with the other, except for one peculiarity in C. neo-zealanica, 

 namely, that the outer margin of the inner lobe of the uropods 

 and the obtuse apex of the caudal shield are thickly ciliated. But 

 the figure shows a pleon consisting of two broad, completely 

 separated, segments, followed by the pleo-telson or caudal shield. 

 By a comparison with the description, it appears as if the first of 

 these segments had been regarded as the seventh of the person, 

 the first peraeon-segment being taken as a portion of the head, 

 which is partially embedded in it. But the second pleon-segment 

 is figured as quite simple, so that, if the figure is to be trusted, it 

 is doubtful whether this species can stand in the genus Cassidina. 

 The same doubt, for a similar reason, will apply to C. maculata 

 Studer. But considering that the authors themselves have not 

 attached any special importance to the characters discussed, there 

 is still at least a possibility that, instead of needing new genera, 

 all the named species of Cassidina may be one and the same. In 

 that case, the ciliated apices in C. neo-zealanica would probably 

 prove to be due to an adventitious growth. It would be very 

 obliging on the part of the authors referred to, or any available 

 representative, if they would re-examine their specimens and 

 publish a decisive account of the required details. 



Cassidina emarginata Guerin-Meneville. 



1843. Cassidina emarginata, Guerin-Meneville, Icon. Begne 

 Animal, Crust., texte, p. 31. 



1853. Cassidina latistylis, Dana, U.S. Expl. Exp. vol. xiii., Crust. 

 p. 784, pi. 52. figs. 12 a-e. 



1871. Cassidina emarginata, Cunningham, Tr. Linn. Soc. Loud, 

 vol. xxvii. p. 499, pi. 59. fig. 4. 



1879. Cassidina emarginata, Miers, Phil. Trans, vol. clxviii. 

 p. 204. 



1884. Cassidina emarginata, Studer, Isopoden Beise ' Gazelle,' 

 p. 19. 



1887. Cassidina emarginata, Pfeffer, Krebse von Siid-Georgien, 

 pp. 63-69, pi. 2. figs. 9-10, pi. 5. figs. 23-30, pi. 6. figs. 1-10. 



