274 THE VOYAGE OF H.M.S. CHALLENGER. 



Length 5 mm., height 6, diameter 2f. 



Habitat. — Station 150, between Kergueleu and Heard Iskinds, in 150 fathoms, 

 coarse gravel ; and off Prince Edward Island, in 100 to 150 fathoms. 



The above is the supposed diameter of a complete shell, being double that of the 

 valve obtained at Station 150, which is presumed not to be adult. It may be only a 

 variety of Mytilus herguelensis, but its form is very different, and the radiating lines are 

 stronw-er and fewer. 



Mytihis herguelensis, n. sp. (PI. XVI. figs. 4-4a). 



Testa parva, solidiuscula, alba, epidermide liavescenti, hirsuta induta, incrementi lineis 

 striata, lirisque tenuissimis, radiantibus instructa, antice acuminata, postice dilatata. 

 Pagina interna alba, nitida. Linea cardinis crassiuscula, edentula. 



This little species may be recognised by its white colour and the brownish-yellow, 

 hairy, or chafty epidermis. It is rather solid, concentrically and radiately striated, 

 narrowed in front and dilated behind. The dorsal outUne is arched without an angle, 

 the ventral being straighter. The interior of the valves is white and somewhat glossy. 

 The hinge-line is rather thick and toothless. 



Length 8 mm., height 5, diameter 3^.. 



Habitat. — Station 149, Royal Sound, Kerguelen Island, on the shore. 



The tips of the umbones in this species are also capped as in Mytilus meridionalis. 



Mytilus (Stavelia) horridus, Dunker. 



Mytilus Jwrridits, Dunker, Proc. Zool. Soc. Land., 18.56, p. 359. 



Mytilus Jwrridus, Reeve, Conch. Icon., vol. x. fig. 9. 



Mytilus tortus, (Dunker) Reeve, loc. cit., fig. 6. 



Stavelia torta, Gray, Pioc. Zool. Soc. Lond., 1858, p. 90, pi. xli. ficjs. 1-1 a. 



Habitat. — Station 186, off Cape York, North Australia, in 8 fathoms (Challenger) ; 

 Cape Capricorn, North Australia, and Island of Mindanao, Philippines (Reeve). 



I agree with Gray in uniting the above species, but do not consider the sinuosity of 

 the ventral margin of generic importance. Reeve states that Dunker described Mytilus 

 tortus in Proc. Zool. Soc. Lond., 1856, but I only there find a mere reference to that name 

 by the latter author in his description of Mytilus horridus, and I have been unable to 

 trace any account of it in any other work. The Challenger shell is very large, being 

 6^ inches in length. 



