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



A few specimens only of this species were met with in a dredging from lat. 35° 39' S., 

 long. 50° 47' W. Depth, 1900 fathoms. 



[PI. XXVII. fig. 4, a-d. a Shell seen from left side, h from above, c from below, 

 d from front. Magnified 50 diameters.] 



Loxoconcha, G. 0. Sars. 



Loxoconcha, Sars, Oversigt, &c., 1865. 

 Nm'mania, Brady, Trans. Zool. Soc, 1865. 



Valves nearly equal, subrhomboidal, mostly flexuous in outline, and evenly convex. 

 Surface smooth, or marked with concentrically arranged impressed puncta, or with 

 polygonal fossae, often also with minute circular papillae. Ventral margins usually 

 forming a prominent compressed keel towards the hinder extremity of the shell ; postero- 

 superior angle obliquely truncate. There is usually a prominent, shining tubercle over 

 the anterior end of the hinge in each valve. Hinge-joint formed by two small teeth at 

 the extremities of the hinge-line of each valve. Limbs of the animal slender and 

 colourless. Anterior antennae very slender, six-jointed, the last joint very long, linear, 

 and bearing long, simple setae ; posterior antennae four-jointed, the third joint long and 

 narrow ; flagellum long and biarticulate, mandible-palp three-jointed, bearing a distinct 

 branchial appendage. Lowest seta of the branchial plate of the first pair of jaws 

 deflexed. Feet long and slender, alike in male and female. Abdomen terminated by 

 a hairy conical process ; postabdominal lobes bearing two moderately long subequal setae. 



The " peach-stone " or obliquely quadrang-ular shape, and the bevelled-off postero- 

 superior angle of the shell, are characters usually sufficiently pronounced to distinguish 

 at a glance the members of this genus. The genus is cosmopolitan, and contains even 

 now a considerable number of recent species, to which we may expect further research to 

 add very largely. In gatherings from between tide marks or from very shallow water it 

 will doubtless be found in greatest abundance. One British species, Loxoconcha elliiotica, 

 occurs only in the brackish water of estuaries and salt-marshes ; and another, Loxoconcha 

 impressa, has occasionally been found in fresh water altogether out of reach of the sea, 

 and in such cases may probably be looked upon as a relic of some old marine fauna. 

 There can be no doubt that the brackish and subbrackish waters of tropical and equatorial 

 countries will some day yield an abundant and highly-interesting harvest to students of 

 the Entomostraca. 



Many fossil species described by authors under various generic terms — Cythere, 

 Cytherina, Bairdia, &c. — belong by rights to Loxoconcha. 



The difierence in shape between males and females is strongly marked, the females being 

 usually tumid, flexuous, and having all their angles, except the postero-superior, well-rounded 

 off" ; the males more compressed, with a flatter dorsal margin, elongated and angular. 



