PLEUROSIGMA. 



[ 608 ] 



PLEUROXUS. 



principally arising from the curvatui'e of 

 one margin of each half of the valve ; keel 

 not median, especially near the ends j ma- 

 rine; length 1-200" ; striie 75. 



StricB longitudinal and transverse (dots 

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



In most of the following species or forms 

 the dots are not ec[uidistaut in the longitu- 

 dinal and transverse rows. 



P. strir/ilis (fig. 12). Linear-lanceolate ; 

 sigmoidiire 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" ; strise, both sets, 38. Fig. 39, piece 

 of valve, showing dots. 



(8. Gradually tapering towards the ends ; 

 striae obscure. 



P. Hippocampus (tig. 13). Narrowly 

 lanceolate, gradually attenuated towards 

 the broad, very obtuse ends ; sigmoidure 

 evident ; keel nearly median ; marine or 

 brackish water ; length 1-lGO"; stritB : long. 

 32, tr. 40. 



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

 Linear-lanceolate, with obtuse ends; sig- 

 moidure slight ; keel nearl)^ median ; marine 

 and freshwater; length 1-120"; striae: 

 long. 30, tr. 40. 



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

 ends rather obtuse ; sigmoidure evident ; 

 keel almost median ; freshwater ; length 

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



P. tenuissimmn (tig. 24). Narrowly linear, 

 attenuate towards the ends ; sigmoidure 

 evident ; keel nearly central ; freshwater ; 

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



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

 sigmoidure evident ; keel nearly median ; 

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

 tr. 50. 



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

 somewhat prolonged ; sigmoidure evident ; 

 keel median ; freshwater ; length 1-180" ; 

 stria) : long. 24, tr. 50, Fig. 42 represents 

 the dots upon part of a valve. 



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

 ceolate, acuminate ; sigmoidure evident ; 

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

 strite : long. 40, tr. 52. 



P.fascioln (tig. 21). Linear-lanceolate; 

 with linear beak-like ends ; sigmoidure evi- 



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

 (?),t;.04. '  o 



P. prolongatum (fig. 23). Very narrowly 

 linear-lanceolate, acuminate, with Hnear 

 beak-like ends ; sigmoidui-e present in the 

 ends only ; keel nearly median ; marine ; 

 length 1-200 ; striae : long. (?), tr. 65. 



P distortmn (jig. 20). Lanceolate; ends 

 slightly produced and beak-like ; sig- 

 moidure evident ; keel central ; marine ; 

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

 " P. macrum (tig. 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 Alcjce.^ 435; 

 Smith, Brit. Diatom, i. 61 ; Kiitzing, Sp. 

 Al(/. and Bacill. ; Rabenhorst, Aly. i. 230 

 (46 European species) ; and the BiBL. of 



DlATOMACE^. 



PLEUROSTAU'RUM,Rab. = Stauroneis 

 united into tilaraents. 



BiBL, Rabenh. Ah/, i. 258; O'Meara, 

 Qu. Mic. Jn. 1872, 387. 



PLEUROT^E'NIUM, Nageli.— A genus 

 of Desmidiaceae, consisting of species of 

 Closterium, Docidium, and Penium. 



BiBL. Rabenh. Fl. Eur. Ala. iii. 140. 



PLEUROT'RICHA, Stein. — A genus 

 of Hypotrichous Infusoria. Like Stylo- 

 nychia.1 but vsathout caudal setae, with 

 larger ventral setfe, and the anal styles in 

 two groups. 3 species ; freshwater. (Kent, 

 Inf. 782.) 



PLEUROT'ROCHA, Ehr.— A genus of 

 Rotatoria, of the family Hydatintea. 



Char. Eyes none ; a single tooth in each 

 jaw; foot forked (^ = Hydatina with uni- 

 dentate jaws). 



P. (jihha (PL 44. fig. 18). Body ovate- 

 oblong, truncate in front ; toes small, turgid. 

 Freshwater ; length 1-216". 



BiBL. Ehr. Infus. 418 ; Gosse, Ann. N. 

 H. 1851. viii. 199. 



PLEUROX'US, Baird. — A genus of 

 Entomostraca, of the order Cladocera, and 

 family Lynceidfe. 



Char. Anterior part of shell prominent 

 above, obliquely truncate below ; first pair 

 of legs very largo ; beak shai'p, cur\ed 

 downwards. Freshwater. 



P. triiioncllus (PL 19. tig. 32). Beak 

 long, sharp-pointed, slightly curved down- 

 Avards ; inferior antennae' short and slender, 

 anterior branch with four seta^, one from 

 the first joint, one from the second, and two 



