I .M PERFECTLY-KNOWN SPECIES OP OSTEACODA. 435 



marginal ridge ; the spaces between, and less conspicuously outside of, these ribs are 

 marked with smaller, curved, anastomosing ridges ; the anterior margin round about 

 the antennal notch (fig. 17) has a thin laminated flange marked by delicate transverse 

 lines. Secondary branch of the antenna (fig. IS) geniculated between the second and 

 third joints ; first joint very short, bearing two short marginal seta;, second and third 

 very long and nearly equal, second with three long seta; on its outer margin, third 

 rugose with a number of wart-like protuberances on its opposing surface, and bearing 

 a single seta near the distal and proximal ends respectively ; extremity blunt and 

 slightly furrowed longitudinally; post-abdominal laminae (fig. 19) armed with three 

 principal ungues and seven smaller ones, the first of the smaller series situated between 

 the second and third larger ones. Length 2'6 mm. 



Hab. Taken abundantly in the surface-net, Otago Harbour. Males only. 



An interesting peculiarity of this species consists in its tendency to develop calcareous 

 concretions on the seta; of the antennas and antennules, and sometimes in other situations. 

 These concretions are extremely dense and dark-coloured, and when broken present a 

 radiated crystalline appearance. Treated with a weak acid, they are seen under the 

 microscope to effervesce freely, and in time to disappear almost entirely, so that they 

 are probably composed chiefly or altogether of calcium carbonate. Two or more seta; 

 are sometimes immovably soldered together by a concretion of this kind, which must, 

 one would think, materially interfere with the locomotion of the animal. Though 

 P. sculpta is especially liable to these concretions, they are sometimes met with in 

 other species; in P. sculpta, however, full-grown specimens seem rarely to be free from 

 them. Though in this gathering the majority of examples had shells of a flexible 

 or membranous kind, some few were distinctly dense and calcareous. These differences 

 may perhaps depend upon the lapse of time in relation to exuviation; but I am 

 disposed to think that in the case of flexible shells there is often a larger development 

 of the concretions above referred to, in which case it may be allowable to look upon 

 them as pathological products which have withdrawn the lime otherwise available for 

 shell-formation. A broken fragment of one of the nodules is shown in fig. 20. It 

 is just possible that a species described by me from one dried shell under the name 

 Streptoleberis crenulata may be identical with P. sculpta, but this I cannot decide 

 with any certainty (see 5, p. 515, pi. iv. figs. 3, 4). 



Philomedes flesilis, sp. n. (Tl. XLIV. figs. 1-14; Plate XLV. figs. 15, 16.) 

 Shell of the female (PI. XLIV. figs. 1, 2 ; PI. XLV. figs. 15, 16), seen from the side, 

 irregularly lozenge-shaped, widest in the middle, greatest width equal to about two- 

 thirds of the length ; anterior extremity somewhat produced and narrowed, beak 

 inconspicuous, antennal notch shallow ; posterior extremity narrowed, running out 

 below the middle into a wide, blunt, and massive tuberosity; dorsal margins boldly 

 arched (in old specimens rugged and ending in a tuberous projection); ventral 

 margin moderately convex. Seen from above, the outline is irregularly polygonal, 



