[22 ] 



slightly projects, distinguishes this 

 genus from. Planorbis; and there 

 being no thickening on the left lip 

 marks it from Natica. Parkinson. 

 Lamarck places the genus in the 

 family Peristomata, order Trachel- 

 lipoda. There are many species, 

 as the Ampullaria patula, Ampul- 

 laria Sigaretina, &c. 



AMY'GDALOID. (apv^Sd\rj } an almond, 

 and eTdos, Gr. amygdalo'ide, Fr.) 

 A volcanic, or igneous, rock of any 

 composition, containing nodules of 

 minerals, scattered through its base, 

 of a roundish shape ; cellular vol- 

 canic rock, having its cells, or 

 cavities, occupied with nodules of 

 a dissimilar substance. 



AHYGBALO'IDAL. Containing rounded, 

 or kernel-shaped, cavities, filled 

 with mineral matter of a different 

 character from the substance gene- 

 rally. 



AMY'GDALYTE. Almond-stone. Of the 

 nature of, or resembling almonds. 



A'NAL. Pertaining to the anus ; the 

 fin between the vent and the tail. 



ANA'LCIME. A simple mineral, a 

 variety of zeolite, with which it 

 was formerly confounded ; it is 

 also called cubizite. It occurs 

 regularly crystallized in angulo- 

 granular concretions, and massive. 

 Specific gravity above 2. "When 

 rubbed, it acquires only a small 

 degree of electricity, and with 

 difficulty. It is composed of silica 

 55-07, alumina 20-22, soda 14'71, 

 moisture 8 '2 8. It is found, in 

 secondary greenstone rocks, in 

 various parts of Scotland, more 

 especially near Edinburgh. This 

 mineral, also called Cubizite, has 

 been regarded by mineralogists as 

 having the cube for its primitive 

 form. Analcime has certainly no 

 cleavage planes, and it must be 

 regarded at present as forming in 

 this respect as great an anomaly 

 in crystallography as it does in 

 optics by its extraordinary optical 

 phenomena. The most common 



form of analcime is the solid, 

 called the icositetrahedron, which 

 is bounded by twenty-four equal 

 and similar trapezia ; and we may 

 regard it as derived from the cube, 

 by cutting off each of its angles by 

 three planes equally inclined to the 

 three faces which contain the solid 

 angle. The Abbe Haiiy first ob- 

 served in this mineral its property 

 of yielding no electricity by fric- 

 tion, and derived the name of 

 analcime from its want of this 

 property. 



A'NALOGTIE. (analogue, Pr. On le fait 

 qutlquefois substantif. Ce sont deux 

 analogues.} Any body which cor- 

 responds with, or bears great re- 

 semblance to, some other body. A 

 recent shell of the same species 

 with a fossil shell, is an Analogue 

 of the latter. Lyell. 



ANA'MESITE. A mineral, a fine-grained 

 dolerite. Its colour is dark grey, 

 or greenish or brownish black. It 

 forms the intermediate step between 

 dolerite and basalt. 



ANANCHY'TES. A helmet - shaped 

 echinus, a fossil of the chalk form- 

 ation. Bakewell. It approaches 

 near to the form of Spantangus 

 globosus. Of the genus Ananchytes, 

 eight species have been determined 

 as occurring in the chalk deposit : 

 one species, ananchytes bicordatus, 

 has been found in the Oxford clay, 

 a member of the oolitic group. 



ANASTOMO'SIS. (anastomose, Pr. anas- 

 tomoso, It. from ava and oro'^a, Gr.) 

 The running of vessels one into 

 another, or communication by in- 

 osculation, as of the arteries into 

 the veins. 



ANASTOHO'SING. Communicating by 

 anastomosis. Applied to vessels, 

 threads, or fibres, which by meeting 

 or touching in separate points only, 

 form a sort of net- work, or reticu- 

 lation. 



A'NATASE. (apaToow, Gr. extension.) 

 Pyramidal titanium; this mineral 

 is nearly of the same nature as . 



