A3IPHDI0RriIINA. 



[ 37 ] 



AMnriSTEGIiNA. 



A. brachiata. Colourless. 



BiBL. Dujardiii, Infus. p. 292. 



AMPHIMOEPIII''NA, Neugeboren.— 

 Oue of the dimorphous Nodosariiie Forami- 

 nifera, in which the t)lder portion has grown 

 on the Froudicularian plan, and the younger 

 chambers are Nodosariau or Dentahne. 

 Tertiary, Germany. 



BiBL. Verhand. Siebejibiiry. 1850. 



AMPHIPEX'TAS, Ehr.— A doubtful 

 genus of fossil Diatomacese (Cohort Anguli- 

 feras). 



Char. Unattached ; frustides cubical, 

 solitary, bi\-alve, and pentagonal. 



A. PeiUacrinus; diam. 1-240"; Greek 

 marl. 



A. alternans (PI. 25. fig. 11) ; Cuba. 



BiBL. Ehrenb. Ber. d. Berl. Ak. 1840 

 and 1843, Abhl. 1841 ; Kutzing,^«c. p. 1.3G; 

 Babenhorst, Alg. i. p. 3J 9. 



AMPHIPLEU'KA, Kiitz.— A genus of 

 DiatomacetB (Cohort Amphipleurefe). 



Char. Frustules free, straight oi- slightly 

 sigmoid ; valves lanceolate or linear-laureo- 

 late, with a median longitudinal line which 

 is thickened and expanded longitudinally at 

 each end, but without a median nodule. 



The valves appear to resemble those of 

 Nitzschia in their inecjuality ; but they are 

 compressed in the opposite direction to those 

 of that genus, and thus the median hues of 

 both valves are visible at once. That the 

 Hues seen upon the frustules are the same as 

 the median lines of the separated valves, is 

 e\ident from their exhibiting the terminal 

 expansions. This view is confirmed by the 

 sides of the frustules being half as broad 

 again as the separate valves. 



A. pellucida (PI. 16. fig. 7a, side view of 

 frustule ; b, of valve). Valves linear-lanceo- 

 late ; length 1-225" ; furnished with longi- 

 tudinal and transverse strite, of extreme 

 delicacy, requiring the best object-glasses of 

 large aperture, and the most oblique light, 

 to render them visible. Sollitt estimates 

 them at 125 to 130 in 1-1000". Nelson at 

 80to 1-1000" longitudinal, and 96tranverse, 

 (by vertical illumination) : Jn. Mic. Soc. i. 

 p. -152, 1881), Freshwater: Brit. 



A. ri(/ida,K. (sif/t)ioidea,Sm.). Marine; 

 valves nan-owly linear-lanceolate, slightly 

 sigmoid ; length 1-150" (PL 16. fig. 7 c, side 

 view) ; British. 



A. Danica, K. Valves lanceolate, trun- 

 cate ; length 1-400" ; coast of Denmark. 



A.injiexa. Marine; linear, lunate, slightly 

 attenuate at ends, obtuse ; length 1-330" ; 

 British. 



A. Lhidheimcri. Larger tiian A. pell. 

 in fr.-wat. torrents, N. Amer. (tSrun, Oestr. 

 Biat. i. p. 469, fig.). 



A. Frauenfddii. Indian Ocean, Grun, 

 ut supra. 



BiBL. Kutzing, Bacill. p, 103; Sp. Alg. 

 p. 88 ; Smith, Brit. Diat. i. p. 45 ; Raben- 

 horst, Flor. Alg. i. p. 143. 



AMPHIPPtU'RA, Ehr.— Agenus of Dia- 

 tomacese (Cohort Naviculese). 



Char. Frustules free, sohtary, constricted 

 in the middle ; valves convex, having a me- 

 dian keel, with a nodule at each end, and 

 either a nodule or stauros in the middle. 



Marine, or inhabitants of brackish water. 



Frustules sometimes much twisted, oc- 

 casionally resembUng a violin in form, from 

 one half of the frustule being in a longitu- 

 dinal plane almost at right angles to that of 

 the other. Surface of the valves more or 

 less distinctly marked with transverse strife, 

 which under high powers and proper mani- 

 pulation are resolvable into dots, arranged 

 as in PI. 15. fig. 8. Many species. 



A. alata, E, Common (PI, 16, fig, 8 a 

 side view ; b, front view), Fr, twisted 

 fr. view linear, ends rounded ; valves nar- 

 rowly elliptical. 



A. constricta, E. Fr. straight, narrow ; 

 valves with a transverse line, ends acute. 



Babenhorst separates the species with a 

 distinctly curved, mostly sigmoid keel, in a 

 genus A?nphka7npa. 



BiBL. Ehr. Abh. Berl. Ak. 1841, p. -333 ; 

 Kutzing, Bacill. p. 107 ; Sp. Alg. p. 93 ; 

 Smith, ^y-i?!. Diat. i. p. 43, ii. p. 92; Greville, 

 Mic. Tr. 1863, pp. 1.3, 20 ; 1865, p. 105 ; 

 Ann. N. Hist. 1865, xvi. p. 5; Gregory, 

 Diat. of Clyde, p. 33 ; Grun, Verh. Wien, 

 1860, p. 569 ; Donkin, Qti. Mic. Jn. 1861, 

 p. 14 ; Rabenhorst, Flora Alg. i. p. 253. 



AMPHISTA, Kent.— A genus of Infu- 

 soria, fam, Oxytrichina, 



BiBL. Kent, Inf. 1880. 



AMPHISO'RUS.— The compound or 

 aged individuals of Orbitolifes orbicnlus, 

 having chambers on both faces of the disk, 

 are grouped by Ehrenberg under this genus 

 of his Bryozoa polysomatia. 



BiBL. Ehrenberg, Abh. Berl. Ak. 1838; 

 Carpenter's For. p. 105. 



AMPHISTEGINA, D'Orb.— One of the 

 high-class genera of Forayninifera perforata, 

 of the Nummuline family. It differs from 

 Nummulina mainly in not being symmetri- 

 cal, one face being more conical than the 

 other. On the flatter face the alar flaps of the 

 chambers are as in Nummulina ; but on the 



