334 BALANID/E, 



2. Tetraclita seurata. PI. 10, fig. 2 a — 2d. 



Shell dark greenish-gray, luith narrow, longitudinal, serrated 

 ribs : radii absent : scutum with the adductor and articular 

 ridges forming a cavity, which runs up to the apex of the valve. 



Jjcib. — Cape of Good Hope ; Algoa Bay ; attached to sandstone and to 

 Patella); Mus. Brit., Cuming, and Stutchbury .* 



General Appearance. — Colour dark greenish gray ; form steeply 

 conical ; surface covered, especially in the lower half of the shell, by 

 numerous, narrow, sharp, longitudinal ridges, but slightly prominent, 

 and serrated or transversely divided into small teeth : when the shell 

 has been much disintegrated, the upper part of the surface consists of 

 the exposed, smooth, rather large, upfilled parietal tubes. I have seen 

 no instance of the development of the radii; sometimes even the 

 sutures are with great difficulty distinguishable, though I believe they 

 ahvays reach the outer surface ; sometimes the sutures are wide from 

 the disintegration of the edges of the compartments. Orifice rounded 

 or oval. 



Scuta. — The scuta and carinal half of the terga are blueish-green. 

 In the scuta neither the articular ridge or furrow are much developed : 

 the adductor ridge is prominent, and is united to the articular ridge, 

 about half way up the latter, thus forming a rather large, triangular 

 cavity, which runs up to the apex of the valve. 



The Terga are beaked. The spur, measured across the upper part, 

 is half as wide as the valve ; it is bluntly pointed ; it is placed quite 

 close to the basi-scutal angle of the valve, so that there is no basal 

 margin on that side; it curves towards the scutum, its extremity ex- 

 tending beyond the basi-scutal angle. 



Structure of the Shell and Radii. — The parietal tubes are rather large, 

 especially those adjoining the inner lamina of the walls. The shell 

 is of singularly little specific gravity, which is due to the parietal tubes 

 not being filled up with shelly matter nearly to so great an extent as in 

 the other species; even in the uppermost part the tubes are not solidly 

 filled up, only their external sides are thickly coated with greenish- 

 black shell, which by corrosion becomes grayish. The radii, as 

 stated, are not developed : the shell breaks with singular facility along 

 the sutures, and the radii are then seen to be most feebly represented 



* I have seen three separate lots of this species all from the Cape of Good 

 Hope ; one lot was collected by Dr. Krauss, at Algoa Bay, and I strongly 

 suspect is the species described by him in his ' Siidafrikanischen Mollusken' as 

 Conia porosa. If the species, figured by Chemnitz, and mentioned in a note 

 (p. 329), under T. porosa, be the present species, the specimens probably did not 

 come from Tranquebar, on which point Chemnitz speaks only from memory. I 

 have seen one specimen ticketed New South Wales, it is possible, considering 

 the case of T. rosea, that this may be correct, but I should like to have further 

 confirmation before giving it as a habitat. 



