168 TETRASTEMMA CANDIDA. 



1846. Prostoma quadrioculata, Johnston. Ann. Nat. Hist., vol. xvi, p. 436. 



„ Polia quadrioculata, De Quatrefages. Ann. des sc. nat., 3 me ser., Zool., torn, vi, p. 216, pi. 11, f. 1 . 



1847. „ „ Prey u. Leuckart. Beitrage z. Kennt. wirb. Thiere, p. 150. 



1849. „ „ De Qnatrefages. Voyage en Sicilie, vol. ii, p. 128, pi. 16, f. 10 and 11. 



1850. Tetrastemma varicolor, Diesing. Syst. Helm., vol. i, p. 257. 

 „ „ grcenlandicum, Ibid. Op. cit., p. 259. 



„ „ Krohnii, Siebold. Archiv fiir Naturges., ii, p. 382. 



1851. „ varicolor, Maitland. Descrip. syst. anim. Belg. septent., p. 190. 

 1853. Vermiculus coluber? var., Dalyell. Pow. Creat., vol. ii, p. 91, pi. 10, f. 24. 



„ Planaria alga, Ibid. Op. cit., p. 117, pi. 16, f. 24 and 25. 



1858. Polia quadrioculata, Williams. Philos. Trans., 1858, p. 131. 



1859. Tetrastemma algce, Leuckart. Archiv fiir Naturges., ii, p. 188. 



1860. Polia obscura (partim), Van Beneden. Mem. Acad. Belg., torn, xxxii, p. 23, pi. 4, f. 2, 4, &c. 

 „ „ capitata, Ibid. Op. cit., p. 28, pi. 4, f. 12, &c. 



„ „ farinosa, Ibid. Op. cit., p. 29, pi. 4, f. 17. 



1861. Tetrastemma varicolor? Claparede. Recher. Anat. snr les Annel. Turb., &c, p. 81, pi. 5, f. 6. 



1862. „ „ (partim), Diesing. Revis. der Turbell., p. 289. 

 ,, „ obscurum (partim), Ibid. Op. cit., p. 291. 



„ „ capitatum, Ibid. Op. cit., p. 292. 



„ „ grcenlandicum, Ibid. Op. cit., p. 293. 



„ „ farinosum, Ibid. Op. cit., p. 293. 



„ Loocorrhochma obscurum, Ibid. Op. cit., p. 295. 



1863. Tetrastemma varicolor, Diesing. Nachtrage zur Revis. der Turbell., p. 10. 

 „ „ algae, Ibid. Op. cit., p. 11. 



1864. Polia quadrioculata, Grube. Die Insel Lussin u. ihre Meeresf., p. 96. 



1865. Tetrastemma varicolor (partim), Johnston. Catalogue Brit. Mus., pp. 20 and 289. 

 „ „ algce, Johnston. Op. cit., p. 20. 



1865-6. Polia quadriocellata, De Quatrefages. Hist. Nat. des Anneles, pi. 4, f. 2. 



1869. Tetrastemma algae, Mcintosh. Trans. Roy. Soc. Edinb., vol. xxv, pt. ii, p. 339 et seq. 



Habitat. — Not uncommon under stones near low-water mark, especially amongst the algae 

 and corallines which cover their surfaces, and, indeed, one of the best modes of procuring the 

 species is to immerse portions of such stones in sea-water, when the animals seek the water- 

 line and are easily observed. It extends from the Shetland to the Channel Islands. 



Body one to one and a half inch long, and nearly a line in breadth ; somewhat flattened, 

 narrowed behind the head, and again tapered towards the tail. 



Colour. — Various shades of grass- or siskin-green, but females bearing ova have a dull 

 grayish aspect. Some varieties, also, are pale yellow. The head is usually paler than the rest 

 of the animal. Two dull red spots indicate the ganglia. A Zetlandic variety occurs in Bressay 

 Sound of a reddish-brown colour, and in some a few white grains are situated between the anterior 

 pair of eyes. 



Head much flattened, spathulate, wider than the succeeding portion of the body, with a pale 

 streak in the median line anteriorly, where there is also a slight notch. Eyes four, forming a 

 square ; by the lengthening of the snout, however, they are placed at the corners of an oblong. 



Cephalic furrows. — The two oblique anterior furrows course inwards near the posterior pair of 

 eyes, and cause a notch at the margin of the snout in front of the latter. The posterior pair were 



