AMPHIMORPIIIXA. 



AMPHISTEGIiNA. 



A. brachiata. Colourless. 



BIBL. Dujardin, In/us, p. 292. 



AMPHIMORPHPNA, Neugeboren. 

 One of the dimorphous Nodosarine Forami- 

 nifera, in which the older portion has grown 

 on the Frondicularian plan, and the younger 

 chambers are Nodosarian or Dentaline. 

 Tertiary, Germany. 



BIBL. Verhand. Siebenbiira.'lSSO. 



AMPHIPEN'TAS, Ehr. A doubtful 

 genus of fossil Diatomaceae (Cohort Anguli- 

 ferae). 



Char. Unattached; frustules cubical, 

 solitary, bivalve, and pentagonal. 



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

 marl. 



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



BIBL. Ehrenb. Ber. d. JBerl. Ak. 1840 

 and 1843, Abhl 1841 ; Kiitziug,-5ac. p. 136 j 

 Babenhorst, Alg. i. p. 319. 



AMPHIPLEU'RA, Kiitz. A genus of 

 Diatomaceae (Cohort Amphiple ureas). 



Char. Frustules free, straight or slightly 

 sigmoid ; valves lanceolate or linear-lanceo- 

 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 inequality ; but they are 

 compressed in the opposite direction to those 

 of that genus, and thus the median lines of 

 both valves are visible at once. That the 

 lines seen upon the frustules are the same as 

 the median lines of the separated valves, is 

 evident 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 ; 6, of valve). Valves linear-lanceo- 

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

 tudinal and transverse striae, 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 

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

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

 p. "152, 1881). Fresh water : Brit. 



A. rigida, K. (sigmoidea, Sm.). Marine ; 

 valves narrowly linear-lanceolate, slightly 

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

 view) ; British. 



A. Danica, K. Valves lanceolate, trun- 

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



A. inflexa. Marine ; linear, lunate, slightly 

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

 British. 



A. Lindheimeri. Larger than A. pell. 

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

 Diat. i. p. 469, fig.). 



A. Frauenfeldii. Indian Ocean. Grun, 

 ut supra. 



BIBL. Kiitzing, Badll. p. 103 ; Sp. Alg. 

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

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



AMPHIPRO'RA, Ehr. A genus of Dia- 

 tomaceae (Cohort Naviculeae). 



Char. Frustules free, soli tary, 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 resembling 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 striae, 

 which under high powers and proper mani- 

 pulation are resolvable into dots, arranged 

 as in PL 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. 



Rabenhorst separates the species with a 

 distinctly curved, mostly sigmoid keel, in a 

 genus Amphicampa. 



BIBL. Ehr. Abh. Berl. Ak. 1841, p. 333 ; 

 Kiitzing, Badll p. 107 ; Sp. Alg. p. 93 ; 

 Smith, Brit. Diat. i. p. 43, ii. p. 92; Greville, 

 Mic. Tr. 1863, pp. 13, 20 ; 1865, p. 105 ; 

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

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

 1860, p. 569 ; Donkin, Qu. 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 Orbitolites orbiculus, 

 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. 



AMPHISTEGI'NA, D'Orb. One of the 

 high-class genera otForaminiferaperfo?*afa, 

 of the Nummuliue 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 



