436 DB. G. S. BEADT ON NEW OE 



with wide extremities and subparallel sides, the laterally-produced rostrum and 

 the posterior beak forming large terminal protuberances. Except in old specimens 

 (PL XLIV. figs. 1, 2) the shell is flexible and membranaceous, and covered with 

 rounded or subangular pittings (fig. 12) ; each valve bears three flexuous longitudinal 

 ribs which, viewed dorsally, stand out very conspicuously as irregular translucent 

 flanges on each lateral margin ; rostrum and adjoining shell-margin bordered with a thin, 

 semitransparent, radially-striated lamina ; posterior extremity fringed with a few very 

 small recurved hairs. Just within the anterior margin, and below the antennal sinus, 

 a small patch of the shell is marked with a series of about ten parallel striee (fig. 18). 

 Fr^tal tentacle (fig. 4) slender, filiform, sharply pointed, its median portion divided 

 into about sixteen very small joints, base bulbously dilated. Secondary branch of the 

 antenna (fig. 6) composed of a single (1) curved, sickle-shaped joint, which bears on its 

 outer edge, near the base, three short setse, near the middle one extremely long plumose 

 seta, and at the blunt apex a short flexuous seta. The setae of the swimming-branch, in 

 small specimens (fig. 7), are short and non-plumose, but in fully-grown ones longer and 

 plumose. The principal chewing segment of the second maxilla (fig. 8) is in the form 

 of a blunt, broad-ended lobe, with one broad tooth-like process at its inner end, and two 

 similar but larger processes at the outer end ; these are sometimes, though not always, 

 of a deep purple colour; spines of the vermiform foot (fig. 9) with very thick 

 peduncles ; post-abdominal ungues about ten in number, progressively increasing in 

 length from the first, which is extremely small (fig. 10) ; the seventh, ninth, and tenth 

 ungues are stout, and bear rather stout and short marginal teeth ; the eighth and all 

 the other ungues are more slender and only feebly ciliated. Eyes usually wanting, 

 but sometimes well developed, deeply pigmented and distinctly visible through the 

 shell (fig. 11). On the inner surface of the rostrum lies a convoluted " shell-gland " 

 which seems to communicate with a nipple-like tubular prominence opening near 

 the margin of the shell (fig. 14). Length 2-2-3 mm. The shell of the male is much 

 narrower and more elongate (fig. 3), but in other respects agrees with that of the 

 female ; the eyes are well developed (fig. 4), and the secondary antennal branch (fig. 5) 

 is very similar to that of P. sculpta. 



Hab. The specimens from which the description is drawn up were taken numerously 

 by the dredge in depths of 1-5 fathoms in Lyttelton Harbour. Others which I refer 

 to the same species occurred in a dredging from 6 fathoms in Akaroa Harbour. These, 

 however, differ slightly from the types in having generally an almost smooth shell with 

 little or no trace of ribs, though in not a few specimens the ribs are quite apparent, 

 and are in character like those of the types. 



The great majority of specimens possess a quite flexible and membranous shell, but 

 two or three (probably very old individuals) occurred in which it had become dense 

 and calcareous, the various processes and ridges being at the same time strongly 

 developed (figs. 1, 2). In some examples, which I suppose to be immature, the 



