PEDIASTRUM. 



[ 582 ] 



PELLIA. 



PEDIASTRUM, Meven. A genus of 

 Desmidiaceae (Confervoid Algae). 



Char. Cells aggregated into a usually 

 circular, minute disk or flattened star, and 

 generally arranged either in a single or in 

 two or more concentric series; marginal 

 cells bipartite on the outside. 



Ralfs describes eleven British species. 

 Interstices of the cells usually hyaline, but 

 in P. seleneeum these are greenish. 



Braun divided the genera into four sub- 

 genera, which include twenty-nine forms 

 more or less worthy of being considered 

 genera. 



P. Boryanum (PI. 14. fig. 48). Cells 

 arranged in one or more circles around one or 

 two central ones ; marginal cells gradually 

 tapering into two long subulate points; 

 notch narrow. Diameter of outer cells 

 1-2730 to 1-2200". 



P. granulatum (PI. 14. fig. 49). Cells 

 six, granular or punctate on the surface; 

 lobes of marginal cells tapering. Diameter 

 of outer cells 1-1850". 



The method of reproduction is noticed 

 under DESMIDIACEJE, p. 244. 



BIBL. Rail's, Br. Desmid. 180; Braun, 

 Rejuv., Ray. Soc. 1853, pis. 3 & 4; Alg. 

 Unicell Gen. Nova, 64; Rabenh. Alg. iii. 69. 



PEDICELLA'RI^E. See ECHINODEB- 



MATA. 



PI. 45. fig. 3 represents a pedicellaria 

 from the common starfish ; the stalk is not 

 figured. 



The bird's-head processes of the Polyzoa 

 (POLYZOA) are analogous organs. 



PEDICELLI'NA, Sara. A genus of 

 Ctenostornatous Polyzoa, family Pedicelli- 

 nidae. 



Char. Those of the family. 



Bodies globose, with a circle of short 

 tentacles, curled inwards and not retractile ; 

 placed at the ends of erect slender stalks 

 springing from a creeping adherent fibre. 

 3 species. 



BIBL. Johnston, Br. Zooph. 381 ; Allman, 

 Polyzoa, Ray Soc., 19, note; Hincks, Pofyz.564. 



PEDICELLINI'D^E. A family of Po- 

 lyzoa, containing the single genus PEDI- 

 CELLINA. 



PEDICI'NUS, Gerv. A genus of Pedi- 

 culidce; with the antennae 3-jointed, the 

 fourth and fifth being fused with the third, 

 the head elongate ; the legs all scansorial ; 

 abdomen broad. On Quadrumana. (Me*g- 

 nin, Paras. 76.) 



PEDICTJLUS, L. A genus of Anoplu- 

 rous Insects, of the family Pediculidas. 



Char. Legs all scansorial or prehensile; 

 thorax large, not constricted from the abdo- 

 men, which has seven segments ; antennae 

 five-joir.tcd ; mouth A\ith a fleshy rostrum. 



The species are human lice. The colour 

 varies according to that of the skin of the 



nle they inhabit ; being darker in the 

 tribes. 



Rostrum retractile, concealed beneath the 

 head, forming a soft tubular sheath dilated 

 at the end, where it is furnished with a 

 double row of hooks, and containing a horny 

 tube formed of four setae. 



P. capitis. Ashy-white, thorax elon- 

 gated, quadrate, abdomen ovate, laterally 

 lobed, segments blackish at the margin. 

 Length of male, 1-10" ; of female, 1-8". 



P. vestimentij bodj r or clothes' louse 

 (PI. 35. fig. 3). Dirty white, elongato- 

 ovate ; head much produced ; thorax con- 

 tracted in front; abdomen with the seg- 

 ments indistinctly indicated. Length about 

 1-8". 



P. tabescentium, distemper-louse. Pale 

 yellow ; head rounded ; antennae long ; 

 thorax large and quadrate; abdomen large, 

 the segments intimately united. Doubtfully 

 British. 



The extraordinary annoyance stated to 

 have been produced by these vermin, has 

 arisen from the want of washing- and puri- 

 fication of woollen garments. 



See PHTHIRIUS. 



BIBL. Denny, Anoplur. ; Murray, EC. 

 Ent. 391 ; Schiodte, Ann. N. H. 1866, xvii. 

 213; M<gnin, Paras. 74: Piaget, Pedicul 

 1880. 



PELARGO'NIUM. See POLLEN, RA- 

 PHIDES, and HAIRS. 



PELEC'IDA, Vuj.,=Loxodes, Cl. & L. 



P. rostrum (PI. 31. fig. 3fy = Lovodes 

 rostrum. 



PELL^E'A, Lk. A genus of Pterideae 

 (Polypodiaceous Ferns). Many species, 

 tropical. (Hooker, Syn. 144.) 



PEL'LIA. A genus of Pellieae (frondose 

 Hepaticae). P. epiplnjlla (fig. 556) is not 

 uncommon in damp shady places, by springs 

 and wells, where it grows rapidly. Its 

 pedicels are silvery-white, the capsules pale 

 brown ; and when the valves are fully ex- 

 panded, the elaters form an elegant tuft 

 m the middle. The character of the frond 

 varies somewhat according to the degree of 

 moisture of the habitat. The forms called 

 longifolia and furcigera are now considered 

 to constitute a distinct species, P. calycina. 



BIBL. Hooker, Br. Jung. pi. 47 ; Br. 



