46 NATURAL HISTORY OF KERGUELEN ISLAND. 



power showing delicate concentric lines and fine radiating, apparently 

 pubescent, lines extending from the umbones. Margins of the shell 

 covered by an extension of the mantle, provided on each side with seven 

 or eight stout cirri or tentacular processes. A single larger cirrus 

 above the foot at the anterior end. Siphon short, foot small, very close 

 to the anterior end of the shell. 



Length, 2 ^°^ ; height, 1.6 ^-^^ 



Habitat, in the channels leading to the oral aperture of a species of 

 Gchinoid {Trijyylus), where it appears to lead a parasitic or at least a 

 commensal existence. These echini were dredged by Dr. Kidder at 

 Eoyal Sound, Kerguelen Island, near the station of the United States 

 observers, in five and twelve fathoms. These tiny mollusks were quite 

 abundant on the particular portion of the echinus mentioned, but none 

 were found on any other part. It would seem as if the soft parts, before 

 becoming contracted by the alcohol, must have almost entirely envel- 

 oped the shell. The latter was of such extreme tenuity that all efforts 

 to remove it entire from the specimens resulted in its destruction. The 

 teeth appeared, however, to resemble those of the other species of the 

 genus ; none of which, so far as I can recall, have been reported as com- 

 mensal animals. 



MODIOLARCID^. 



KIDDERIA, n. g. 



Shell minute, byssiferous, concentrically sculptured, with two minute 

 cardinal teeth in each valve, and a partially internal ligament attached 

 to a more or less prominent process on the inner hinge-margin of each 

 valve. Pallial line simple. 



KiDDEEIA MINUTA, n. S. 



Mus. No. 11908. 



Shell minute, thin, inflated ; shaped not unlike a short LitJiodomus ; the 

 upper i^osterior surface dark rose-color, the basal and umbonal portions 

 of the valves whitish, with an excessively thin epidermis ; the interior 

 more or less suffused with rose-color, smooth, but not polished. Muscular 

 scars indistinct, anterior scar rounded, posterior ovate. Umbones 

 rounded, inflated, nearly terminal ; anterior end of shell subtruncate, 

 posterior end rounded. Surface smooth, under a high i)0wer showing 

 minute rounded incremental concentric ridges. Cardinal teeth very 

 minute, anterior largest, hinge-margin not thickened except at the liga- 

 mentary processes. Ligament strong and thick, attached almost exclu- 



