E Q U 



ERR 



distinct genus Calamites. Equisetacoce 

 are found from Lapland to the Torrid 

 Zone ; its species are most abundant in 

 the temperate zone : as we approach a 

 more frigid temperature they diminish in 

 size and abundance, and in the warm and 

 humid regions of the tropics they acquire 

 their greatest magnitude. 



ECIUISE'TUM. (Lat. A genus of the or- 

 der Filices, belonging to the Cryptogamia 

 class of plants.) Horse-tail. Of this 

 genus there are numerous species. The 

 equisetum fluviatile of our marshes is the 

 largest of all the species, growing some- 

 times to the height of three feet, and 

 nearly an inch in diameter. It has a suc- 

 culent, erect, jointed stem, with attenuated 

 foliage surrounding the joints in whorls. 

 In the coal measures, remains of equiseta 

 are in great abundance, and occur of a 

 magnitude quite unknown at the present 

 day, some of the stems being fourteen in- 

 ches in diameter. M. Ad. Brongniart 

 enumerates twelve species of calamites 

 and two of equiseta found in strata of 

 the carboniferous series. Equiseta occa- 

 sionally occur in the Wealden strata, and 

 where they are found they are abun- 

 dant. 



ECIUISE'TUM LYELLII. The name given 

 by Dr. Mantell to a distinct species of 

 equisetum, found in the grey and blue 

 grit and limestone at Pounceford, in ho- 

 nour of Professor Lyell. When perfect, 

 it probably attained a height of two feet 

 or more. This plant is beautifully fi- 

 gured in Dr. Mantell' s " Geology of the 

 South-east of England." 



ECIUISE'TIFORM. (from equisetum and 

 forma, Lat.) Having the shape of 

 equisetum, or horse-tail ; resembling equi- 

 setum. 



EQUIVALENT, (from eequus and valens, 

 Lat.) In geology, where one bed sup- 

 plies the place of another which, in that 

 situation, is wanting, such bed is called 

 the equivalent of the wanting bed. When 

 a stratum suddenly terminates, and its 

 place is supplied by a stratum of a dif- 

 ferent character, the latter is called the 

 equivalent of the former. In the beds 

 of transition limestone at Llanymynah, 

 says Mr. Bakewell, which are very re- 

 gularly stratified, one stratum of the best 

 limestone suddenly terminates, and its 

 place is supplied by a bed of marie of 

 equal thickness ; in this case the marie is 

 the equivalent of the absent limestone. 



E'auiVALVE. (fromaquus and valva, Lat.) 

 In conchology, when the shells of bivalves 

 are formed exactly alike, as regards their 

 length, width, depth, &c. The shells of 

 mya, solen, tellina, &c., are generally of 

 the kind called equivalve, while those of 

 ostrea, pinna, &c., are inequivalve. 



E'RA. (cera, Lat. Written frequently <z>ra.) 

 A particular account and reckoning of 

 time and years, from some remarkable 

 event. Webster, quoting from some 

 encyclopaedia, says, " it differs from 

 epoch in this ; era is a point of time fixed 

 by some nation or denomination of men ; 

 epoch is a point fixed by historians and 

 chronologists. The Christian era began 

 at the epoch of the birth of Christ." 



ERADIA'TION. (from e and radiatio, Lat.) 

 Emission of rays. 



ERE'CTILE. (from erigo, Lat.) A tissue 

 peculiar to certain parts of the body, as 

 the nipple, &c. 



ERE'CT. (emtfw*, Lat.) In botany, leaves 

 are so called when they form a very acute 

 angle with the stem. The term also is 

 applied to branches rising in an upright 

 direction ; to petioles rising nearly per- 

 pendicularly ; and to flowers and pedicles 

 rising perpendicularly. 



E'RINITE. A name given to a species of 

 native arseniate of copper, from its hav- 

 ing been discovered in Ireland. It is of 

 an emerald-green colour ; its constituent 

 parts are oxide of copper, arsenic acid, 

 alumina, and water. 



ERO'DED. (erodo, Lat.) Eaten away: 

 corroded. 



ERO'SION. (erosio, Lat.) 



1. The act of gradually wearing away. 



2. The state of being gradually eaten away 

 or corroded. 



ERO'SIVE. That has the property of gra- 

 dually eating away. 



ERO'SE. ) (erosus, Lat.) Jagged ; applied 



ERO'SUS. 5 to leaves very irregularly 

 cut or notched, and having the appear- 

 ance of being gnawed or eaten by in- 

 sects. 



ERO'TYLUS. A genus of insects, belong- 

 ing to the Vivalpi, or the seventh family 

 of the Tetramera. In the erotyli the 

 intermediate joints of the antennae are 

 almost cylindrical, and the club, formed 

 by the last ones, is oblong ; the interior 

 and corneous division of their maxillae is 

 terminated by two teeth. They are pe- 

 culiar to South America. 



ERINA'CEUS. (Lat.) The hedgehog. 



ERPETO'LOGIST. (from erpetology.} One 

 who studies, or is skilled in, that branch 

 of natural history, which relates to rep- 

 tiles. 



ERPETO'LOGY. (from tpTrt roc and Xoyoc, 

 Gr.) That branch of natural history 

 which treats of the structure, habits, &c. 

 of reptiles. 



ERRA'TIC. (erraticus, from erro, Lat. 

 erratique, Fr. erratico, It.) Wandering ; 

 not fixed ; irregular. 



ERRA'TIC BLOCK GROUP. One of the sub- 

 divisions of detrital deposits. Professor 

 Phillips observes, " In the British islands, 



