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



in the left, with generally, especially in young shells, a second very small oblique slender 

 one posterior to the other. The ligament-plates (nymphse) are moderately developed 

 and more or less obliquely roughly striate, and somewhat grooved lengthways. From 

 this desciption it will be seen that the hinge of this species coincides exactly with that 

 of P.sammohia. The pallial sinus is very deep, reaching almost to the anterior scar. 

 Tellina silicula, Deshayes, and TelUna compta, Goulrl, are absolutely identical in every 

 respect, and are more closely and more obliquely striated than some other forms of the 

 species. Tellina pura, H. Adams, and Tellina hi/aria, Baird, agree with one another in 

 colour, lacking the rosy rays of the two above mentioned varieties. 



The distribution of this pretty shell is as extended as its colour is variable. Tt has 

 already been recorded from the Philippine and Mariana Islands, New Caledonia, and the 

 Gulf of Suez, and in the British Museum there are specimens from the Keeling and Fiji 

 Islands, and also Madagascar. 



Tellina (Arcojyagia) pretiosa, Deshayes. 



TeHina jnvtiosa, Deshaye?, Proc. Zool. Soc. Lond., 1854, p. 360. 

 Tellina pretiosa, Sowerby, Conch. Icon., vol. xvii. fig. 329. 

 Tellina costata, Sowerby, lor. cit., fig. 19-i. 



Habitat. — Levuka, Fiji Islands, in shallow water (Challenger) ; Island of Ovalau, 

 Fiji, in 12 fathoms, sandy bottom (Brit. Mus.) ; Philippine Islands. 



There is no Hkelihood of this charming species being confounded with any other. It 

 is well distinguished from all others by the beautifully scj^uamate costellse which adorn 

 the surface. These are somewhat variable in number and thickness, those (about forty) 

 in the type from the Philippine Islands being a little stouter and less numerous than 

 those of Fiji examples, the latter, in this respect, agreeing perfectly with the shell 

 figured by Sowerby as Tellina costata. Between these radiating ridges are very fine 

 concentric thread-like lirse, which pass up the sides of the former, and on the top are 

 produced into scale-like processes, so that the valves, especially near the umbones, have 

 a cancellated aspect. The colour is grey-white, varied with an opaque-white short ray at 

 the apex of the l)eaks. The interior is either pure white or faintly tinged with yellow 

 at the upper part. The texture of the shell is thin, so that the cancellated character of 

 the external ornamentation is distinctly visible within. The lateral teeth are rather 

 strongly developed on each side in both valves, each also having two cardinals. In the 

 right the posterior tooth is twice as large as the anterior, and is bifid, as is also the front 

 one in the left valve, in which the hinder tooth is inconspicuous in comparison with the 

 rest. The pallial sinus is not very large, extending only a little beyond the middle of 

 the valves. The outline at first ascends on leaving the sear, then descends obliquely, 

 and finally slants backwards, forming rounded angles where the direction changes. 



The largest specimen is 17 mm. long, 12^ high, and 6^ in diameter. 



