Naoiculacea.'] infusoeial animalcules. 427 



acute, median line central; colour a clear straw. Length l-75th. 

 Breadth l-920th. Striae l-44,000th apart. Poole Bay, Lewes, and 

 Hull. (P. 19, f. 4.) 



Pleueosigma dilicatulum. — ^^'alvc narrow, lanceolate; flcxiu-e slight, 

 extremities acute ; colour* veiy pale straw, with a slight tinge of 

 pink. Length l-112th. Breadth l-1500th. Stiite 1 -50,000th apart. 

 More delicate than the last; sti-iaj veiy indistinct (P. 19, f. 5.) Lewes. 



P. strigosum. — Yalve lanceolate, flexure slight, cxti-emities obtuse, 

 colom- straw. Length l-90th. Brcadth l-800th. Striss l-38,000th 

 apart. Coast of Sussex, Hull, &c. (P. 19, f. 6.) 



P. anriiilatiim. — Yalve broadly lanceolate or quadrangular, extremi- 

 ties acute, flexm-e moderate; colour a bright chestnut. Length 

 1-llOth, Brcadth l-428th. Stri» l-45,000th apai't, (P. 19, f. 7.) 



Yar. fh.J — Yalve ntuTOw, lanceolate, slightly quadrangular (P. 19, 

 f. 8) = Xavimla JEstmni (Kiitz.) 1849. 



Var fc.J — Yalve much smaller, quadi'angular (P. 19, f. 9) 



" The quadrangular form of this species is always more or less 

 present, and seems to distinguish it from all its alHes." 



P. distortum. — Yalve lanceolate, abruptly bent towards the obtuse 

 extremities ; coloiu* a very pale pink ; striae obscure. Length 

 l-320th. Breadth l-1500th. Coast of Sussex. Probably the young 

 of some other species (P. 19, f. 10.) 



P. obscurum. — Yalve Hncar, slightly attenuated towards the obtuse 

 extremities ; median line not central ; colour veiy pale pink ; stria) 

 obscure. Length l-193rd. Breadth l-2000th (P. 19, f. 11.) Poole 

 Bay and Lewes. 



Yar. fbj much smaller, more gradually attenuated (P. 19, f. 12.) 

 Poole Bay, covering a sponge. 



* * Beads ojp^osite ; sfn'ce transverse and lo7igitvdmal ; all marine. 



P. Balticum. — Yalve linear, straight, suddenly attenuated towards 

 the sigmoid extremities, "which are somewhat obtuse ; coloiu' dark 

 brown. Length l-83rd. Brcadth l-850th. Striae l-38,000th apart, 

 (P. 20, f. 1 and 17.) 



Yar. /^ J.;— Smaller, gradually attenuated (P. 20, f. 2,) 



Yar. fy.) — Much smaller, attenuated throughout; stria? obscure 

 (P. 20, f. 3. 



F r 2 



