PLEUROSIGMA. 



[ 608 ] 



PLEUROXUS. 



principally arising from the curvature of 

 one margin of each half of the valve ; keel 

 not median, especially near the ends ; ma- 

 rine ; length 1-200" j striae 75. 



Stria longitudinal and transverse (dots 

 opposite, PI. 15. figs. 39, 42). 



In most of the following species or forms 

 the dots are not equidistant in the longitu- 

 dinal and transverse rows. 



P. striyilis (tig. 12). Linear -lanceolate ; 

 siginoidu're evident ; keel nearly median, 

 flexure double; marine; length 1-75"; 

 striae : longitudinal 40, transverse 36. 



P. balticum (fig. 10). Broadly linear, 

 narrowed at the ends ; sigmoidure apparent 

 at the ends only and produced principally 

 by the curvature of one margin only ; keel 

 not median, flexure double ; marine ; length 

 1-80" ; striae, both sets, 38. Fig. 39, piece 

 of valve, showing dots. 



]3. Gradually tapering towards the ends ; 

 striae obscure. 



P. Hippocampus (fig. 13). Narrowly 

 lanceolate, gradually attenuated towards 

 the broad, very obtuse ends ; sigtnoidure 

 evident ; keel 'nearly median ; marine or 

 brackish water ; length 1-100" ; striae : lo.ig. 

 32, tr. 40. 



P. attenuatum (fig. 15. PI. 1. fig. 17). 

 Linear-lanceolate, with obtuse ends; sig- 

 moidure slight ; keel nearly median ; marine 

 and freshwater ; length 1-1 20" ; striae : 

 long. 30, tr. 40. 



P. lacustre (fig. 18). Linear-lanceolate, 

 ends rather obtuse j sigmoidure evident ; 

 keel almost median; freshwater; length 

 1-130" ; strise, both sets, 48. 



P. tenuissimum (fig. 24). Narrowly linear, 

 attenuate towards the ends; sigmoidure 

 evident; keel nearly central; freshwater; 

 length 1-180" ; strife, both sets, 48. 



P. Spencerii (fig. 17). Linear-lanceolate ; 

 sigmoidure evident ; keel nearly median ; 

 freshwater ; length 1-200" ; striae : long. 55, 

 tr. 50. 



P. littorak (fig. 19). Lanceolate, ends 

 somewhat prolonged ; sigmoidure evident ; 

 keel median; freshwater; length 1-180"; 

 striae : long. 24, tr. 50. Fig. 42 represents 

 the dots upon part of a valve. 



P. acuminatum (fig. 14). Linear-lan- 

 ceolate, acuminate ; sigmoidure evident ; 

 keel median; freshwater; length 1-150''; 

 striae : lotfg. 40, tr. 52. 



P.fasoiola (fig. 21). Linear-lanceolate ; 

 with linear baak-like ends ; sigmoidure evi- 



j dent j marine ; length 1-200" ; striae': long. 

 ! (?),tr.64. 



P. prolongation (fig. 23). Very narrowly 

 linear-lanceolate, acuminate, with linear 

 beak-like ends ; sigmoidure present in the 

 ends only ; keel nearly median ; marine ; 

 length 1-200 ; striae : long. (?), tr. Go. 



P. distortion (fig. 20). Lanceolate; ends 

 slightly produced and beak-like ; sig- 

 moidure evident ; keel central ; marine ; 

 length 1-300''; striae: long. 65, tr. 75. 



P. macrum (fig. 22). Very narrowly 

 linear-lanceolate ; ends produced into long 

 beak -like processes; sigmoidure produced 

 by the ends of the beaks only ; keel median ; 

 length 1-100"; marine; striae: long. (?), 

 tr. 85. 



BIBL. Hassall, Freshwater Alga, 435; 

 Smith, Brit. Diatom, i. 01 ; Kiitzing, Sp. 

 Alg. and Bacttl. ; Rabenhorst, Alg. i. 230 

 (46 European species); and the BIBL. of 



DlATOMACEJB. 



PLEUROST AU'RUM,Rab. = Stauroneis 

 united into filaments. 



BIBL. Rabenh. Alg. i. 258; O'Meara, 

 Qu. Mic. Jn. 1872, 387. 



PLEUROT^E'NIUM, Nageli. A genus 

 of Desniidiaceae, consisting of species of 

 Closterium, Docidium, and Penium. 



BIBL. Rabenh. Fl. Eur. Alg. iii. 140. 



PLEUROT'RICHA, Stein. A genus 

 of Hypotrichous Infusoria. Like Stylo- 

 nychia, but without caudal setae, with 

 larger ventral set*e, and the anal styles in 

 two groups. 3 species ; freshwater. (Kent. 

 Inf. 782.) 



PLEUROT'ROCHA, Ehr. A genus of 

 Rotatoria, of the family Hydatinaea. 



Char. Eyes none ; a single tooth in each 

 jaw; foot forked ( = Hydatina with uni- 

 dentate jaws). 



P. gibba (PI. 44. fig. 18). Body ovate- 

 oblong, truncate in front ; toes small, turgid. 

 Freshwater ; length 1-216". 



BIBL. Ehr. Infm. 418 ; Gosse, Ann. N. 

 H. 1851, viii. 199. 



PLEUROX'US, Baird. A genus of 

 Entpmostraca, of the order Cladocera, and 

 family Lynceidae. 



Char. Anterior part of shell prominent 

 above, obliquely truncate below ; first pair 

 of legs very large ; beak sharp, curved 

 downwards. * Freshwater. 



P. triganellus (PI. 19. fig. 32). Beak 

 long, sharp-pointed, slightly curved down- 

 wards ; inferior antennae short and slender, 

 anterior branch with four setae, one from 

 the first joint, one from the second, and two 



