REPORT ON THE ISOPODA. 119 



Family Tanaid^e. 



Tanais, Milne-Edwards. 



Tanais, Milne-Edwards, Resume d. Ent.,.p. 182, 1829. 



Anisocheirus, Westwood, Ann. d, Sci. Nat., t. xxvii., 1832. 



Zeuxo, Templeton, Trans. Entom. Soc. Lond., vol. i p. 203, 1836. 



Crossurus, H. Rathke, Nova Acta Acad. Cass. Leop. -Carol. Nat. Cur., vol. xx. p. 35, 1843. 



Two different species were obtained by the Challenger that are referable to the genus 

 Tanais, as redefined by Sars ; one of these was noticed by the late Dr. v. Willemoes- 

 Suhm for the peculiarity that the eggs are carried by the female in two sacs attached to 

 the bases of the last thoracic limbs, much after the fashion of a Copepod ; the ovigerous 

 lamella? of the anterior thoracic segments remain undeveloped. This particular species 

 has been lately described by Dr. Studer and named Tanais willemoesii. A second species 

 of the genus tv as dredged, also in shallow water, off Prince Edward Island. 



Tanais willemoesii, Studer. 



Tanais sp., Suhm, Proc. Roy. Soc. Lond., vol. xxiv. p. 590. 



Tanais willemoesii, Studer, Isopoden gesammelt, etc., Abhandl. d. k. Akad. d. Wiss. Berlin, 

 1883, p. 24 (of Memoir). 



A very large number of specimens of this species were dredged off Kerguelen Island in 

 shallow water; as, however, the species has been recently carefully described by Studer, it 

 is hardly worth while to recapitulate his description here. This is the species to which the 

 late Dr. v. Willemoes-Suhm referred in his Preliminary Report in the following words : — 



"A Tanais having a length of about 17 millims. is very common, and though not 

 deviating by any means from the typical species of the genus, it has a peculiarity 

 connected with its propagation ; for the females, instead of having breeding-laniellas, as 

 the other species of the genus have, carry their eggs, like Copepods, in small cutaneous 

 sacs attached to the genital opening at the base of the fifth pair of pereiopods. These 

 sacs extend as the development goes on, and attain a diameter of 3-4 millims. Professor 

 Wyville Thomson having discovered among the echinoderms of Kerguelen Land many 

 forms which do not undergo any metamorphosis, but develop in pouches of their parents, 

 this peculiarity in Tanais deserves to be noted, not exactly as comparable to those facts, 

 but as an anomaly in the group to which the animal belongs." 



Among the individuals collected by the Challenger there were a large number of 

 females, some with fully develojaed egg-bags filled with eggs, and others in which these 

 structures were still rudimentary ; in no case, however, were there any observable traces 

 of ovigerous laniellse on any segments other than the fourth. 



Station 149k, off Christmas Harbour, Kerguelen, January 29, 1874; lat. 48° 40' S., 

 long. 69° 6' E.; depth, 45 fathoms ; volcanic mud. 



