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



posteriorly it is tlie slightest excurved, in I'rout it is a trifle concave. The lower out- 

 line is broadly arcuate, and forms in front with the dorsal margin a rather sharply 

 rounded extremity, and posteriorly joins the upper margin in an indistinct rounded 

 angle. The umbones are small, acute, very little elevated, and placed a little in front 

 of the centre. The central cardinal tooth in each valve is triangular and large, the 

 anterior in the right is smaller than that of the left, the posterior in the latter is more 

 slender than the corresponding tooth in the former, and the lateral tooth in the left 

 valve is conical, elongate, and compressed. The muscular scars are rather deep and high 

 up, the anterior, which is elongate, commencing immediately beneath the lateral tooth. 

 The posterior scar is broader, and the pallial sinuation is moderately wide but very 

 shallow. The margin of the valves is flattened within, except along the hinder dorsal 

 slope and the lunule, where it is linearly grooved. The lunule is lanceolate, circum- 

 scribed by a distinct impressed line, not affected by the radiating sculpture, but merely 

 sti'iated by fine lines of growth, as is also the case with the narrow posterior area, 

 which is limited by roundly keeled margins. The ligament is small and subinternal. 



Length 8f mm., height 7^, diameter 4. 



Habitat. — Station 172, off Nukalofa, Tongatabu, in 18 fathoms; coral mud. 



Circe fastigiata (Sower by). 



Cytherea fastigiafa, Sowerby, Tliesaurus, vol. ii. p. 643, pi. cxxxv. figs. 158, 159. 

 Circe fastigiata, Eeeve, Conch. Icon., vol. xiv. fig. 11. 



Habitat. — Cape York, North Australia, in 3 to 12 fathoms. 



A single small valve only was obtained at this locality. It agrees with Circe 

 fastigiata of Sowerby, which in my judgment is probably only a peculiarly painted 

 variety of the well-known Circe incta of Lamarck, and I am of opinion that when our 

 series of specimens from numerous localities has become considerably larger than at 

 ])resent, there will be great difliculty in separating these two forms, in addition to Circe 

 tigrina, Lamarck, Circe trimaculata, Lamarck, Circe sidcatina, Lamarck, and 

 Circe hieroglypMca, Conrad. 



The shell depicted by Romer (Monog. Venus, vol. i. pi. xlv. figs. 1-lc) as Circe 

 fastigiata is not Sowerby's species, but rather a foim of Circe tigrina. 



Circe gordoni, n. sp. (PI. II. figs. 5-5e). 



Testa subtrigona, valde ina^quilateralis, nitida, antice brevis, rotundata, postice 

 angustata, producta, subrostrata, mediocriter inflata, omnino alba, vel lineis rufis 

 Iransversis angulato-undulatis picta, liris concentricis, umbones lateraque versus perspicuis, 



