ARACHNOSPIS, 



[ 70 ] 



ARCELLA. 



valves plane or slightly convex, with radia- 

 ting and concentric lines (rows of dots), and 

 a central pseudo-nodule. 



The markings upon the inner valves are 

 not the same as those upon the outer (or 

 parent) : hence the mere variations of the 

 markings are not characteristic ; nor is the 

 number of rays constant. 



A. ornatus, Ehr. Valves very finely gra- 

 nular ; rays29,equal. In Patagonian guano. 



A. Ehrenherfiii, Bail. I'seudo-nodule sur- 

 rounded by an inner ring of linear radiating 

 and an outer ring of circular or angular 

 markings (depressions) ; marine ; breadth 

 1-200 to 1-60" ; occurs also in guano. (PI. 

 16. figs. 12 & 1.3, side view.) 



A. mdicus (PI. 51. fig. 3). J &^^\^ ^^ 



^ • 7 • /-m '1 £ <\ <iNicobar 

 A. mcobaricus (PI. ol. hg. 4). j, i 



BiBL. Ehr. Be): d. Berl. Ak. 1848 & 

 1849 ; Smith, Br. Diat. i. p. 25 ; Shadbolt, 

 TV. Mic. Soe. iii. ; Arnott, Micr. Jn. 1858, 

 p. 159 ; Greville, Micr. Tr. 1865, p. 47. 



ARA.CHN0S'P1S, Kent.— A genus of 

 Infusoria, fam. Halteriidas. 



BiBL. Kent, Infus. p. 214. 



ARACHNU'LA, Cieuk.— A genus of 

 Rhizopoda. 



Char. Naked, colom-less, without nucleus ; 

 one or more contractile vesicles ; pseudo- 

 podia branched, very slender, anastomosing; 

 bodies connected by thickish cords. Move- 

 ment active. 



A. impatiens. In brackish water. Black 

 Sea. 



BiBL, Cienkowski, ScJi. Arch., 1876, xii. 

 p. 27. 



ARANE'IDA.— A family of Arachnida, 

 comprising the true spiders. 



The species of genera belonging to this 

 family ( as A. civilis and domestica, house- 

 spiders, Epeira diadema, garden-spiders &c.) 

 are readily accessible for examining the 

 structural peculiarities of spiders — the skin, 

 the eyes, the organs of the mouth, the max- 

 illarv palpi, the spinnerets, the legs, &c. 

 (See PL 0.) 



BiBL.Walcken., ^p^eres, i.; \\oc\\, Arachn. 

 viii. ; Treviranus, Bau d. Arachn. ; Walker, 

 Brit. Spiders ; JNIurray, Ec. Ent. p. 43. 



ARAUC A'RI A, Jussieu.— A genus of Co- 

 niferse (Gymnospermous Flowering Plants), 

 remarkable for the character of the markings 

 on the walls of the cells of the wood, where 

 the pits or bordered pores appear in two or 

 more parallel rows (PI. 48. fig. 5). Arau- 

 earia {Eufassa) exceha is the Norfolk- Island 

 Pine, which grows to an immense size, as 



do also A. hrasiliensis, A. imhricata, &c. 

 The reservoirs of turpentine seem to be in 

 the bark and not in the wood. See Coni- 

 fer.^, Wood, and Secondary Layers. 



ARAUC ARI'TES, Goeppert (Dado.vylon, 

 Endlicher ; Pinites, Lindl. and Hutt.). — A 

 genus of Fossil Coniferae, characterized by 

 a structure resembling that of Araucaria. 



BiBL. Witham, Fossil Vef/elahles, p. 72, 

 pi. 4-11. Edinb. 18.33 ; Lindley aud Huttou, 

 Fossil Flora, l.t. 2,3. 



ARCEL'LA, Ehr.— A genus of Rhizo- 

 poda, of the family Arcellina. 



The Arcellfe correspond to Amoebae con- 

 tained in a carapace. In some species the 

 carapace is membranous and uniform ; in 

 others it is calcareous and exhibits fine striae, 

 depressions, or granides spirally arranged. 



A. vidgaris (PI. 30. fig. 14a). Carapace 

 brownish yellow, plano-convex, or hemi- 

 spherical, covered with depressions. These 

 markings or depressions are very beautiful 

 and interesting. They agi-ee with those 

 upon the valves of the Diatomaceae in re- 

 gard to the requirements for their display ; 

 with unilateral oblique light, lines only are 

 visible. Their true structure resembles that 

 in PL 15. fig. 41, or PL 17. fig. 29, except 

 that the rows are somewhat wa'vy or even 

 spiral. Fr. wat. ; breadth 1-500 to 1-200". 

 In the young state it is very transparent and 

 pale,'and the markings are with diiliculty di- 

 stinguished. The shell is cast several times 

 before arriving af maturity. PL 32. fig. 24 

 represents the animal with its processes pro- 

 truding from the carapace. 



We have seen two of these animals con- 

 jugating, and so firmly united by the soft 

 internal substance, that they were not sepa- 

 rable by rolling them over between two 

 plates of glass. 



A. (Ec/iitiopi/xis) acvleata (PL 30. fig. 

 14 Z>). Carapace brownish, discoidal, con- 

 vex above, with one or more irregular spi- 

 nous prolongations at the margin ; fr. wat. ; 

 breadth 1-200" without the spines. 



A. dentata (PL 30. fig. 14 c). Hemi- 

 spherical, anguloso-polygonal ; carapace 

 membranous, homogeneous, vollowish or 

 greenish ; fr. wat. ; breadth 1-560 to 1-200". 



A. aureola (Ci/phidixin auroleum, Ehr.) 

 (PL 30. f. 38). C'arapace yellow, angular, 

 with numerous tubercles, four of which are 

 larger and more projecting ; a single expan- 

 sion of varied size ; breadth 1-560 to l-420"j 

 fr. wat. Fig. 38 a represents the carapace 

 viewed from above, b the same supported 

 upon one angle, and t\ie single expansion. 



