DIP 



[141 ] 



D I S 



eluded that although the genus 

 Dipterus ought to be retained, the 

 supposed four species are only 

 differently modified forms of the 

 same animal. The generic charac- 

 ter of the Dipterus, as now con- 

 firmed by M. Agassiz, consists in 

 " two dorsal fins opposite to two 

 similar anal fins, with a caudal fin 

 conforming to that of the genus 

 Palaeoniscus, in having the verte- 

 bral column prolonged into the 

 extremity of the tail." The dip- 

 terus is a characteristic fossil of 

 the tilestone. The dipterus differs 

 from the osteolepis chiefly in the 

 position of its fins, which are 

 opposite, not alternate ; the double 

 dorsals exactly fronting the anal 

 and ventral fins. 



DIPT'BE. (from Svo two, and ?rvp, fire, 

 indicating the double effect of 

 fire to produce fire and phosphor- 

 escence in this mineral. It is 

 generally classed with scapolite.) 

 The schmelzstein of Werner, 

 A mineral, a variety of scapolite 

 found in the Pyrenees, thus named 

 by Haiiy. It consisists of silica 

 60*0, alumina 24-0, lime lO'O, and 

 some water and loss. 



DIRECTION-. In geology, a term 

 applied to the course which strata 

 take at right angles to their line of 

 dip. De la, JBeche. 



Disc. | (diseus, Lat.) 



DISK. ) 1. In conchology, the 

 middle part of the valves, or that 

 which lies between the umbo and 

 the margin ; the convex centre of 

 a valve, or most prominent part of 

 the valve, supposing it to lie with 

 its inside undermost. 

 2. In botany, the central florets of 

 a compound flower; the whole 

 surface of a leaf. 



DI'SCINA. A genus of recent ovate, 

 unequal, roundish bivalves. 



DISCO'POBA. A genus of cellepora, 

 found recent only, and differing 

 from tubulipora in the cells being 

 more sunk and less free ; and from 



cellepora in having no lobated, 

 convoluted, or ramose expansions. 



DISCO'BOLI. The name given to a 

 family of fishes, in Cuvier's ar- 

 rangement, from the disk formed 

 by their ventrals. The fishes of 

 this family form two genera. 



Di' SCOLD. | 1. In the form of a disc. 



DISCOI'DAL. ) In botany, plants, the 

 petals of whose flowers are set so 

 closely and evenly as to make the 

 surface plain and flat like a dish. 

 2. In conchology, when the whorls 

 are so horizontal as to form a 

 flattened spire. 



DISCOI'DES. A genus of fossil echinus, 

 one species only of which has been 

 found, namely discoides subuculus. 



DistfopHORA. The third order of the 

 class annulata. 



DISCO'EBIS. A genus of microscopic 

 spiral discoidal univalves. 



These have been thought by some 

 authors, and the number includes 

 Lamarck, to be found in a fossil 

 state only; but Parkinson states 

 that they are found recent on our 

 coasts. 



DISCOBBI'TES. Fossil shells of the 

 genus discorbis. 



DISCO'POBA. The name given by 

 Lamarck to a genus of fossil corals. 

 Three species are described as be- 

 longing to the Wenlock limestone, 

 namely, D. antiqua ; D. squamata ; 

 and D. favosa. The two last have 

 been thus named by Mr. Lonsdale. 



DISI'NTEG BATED. Separated into in- 

 tegrant parts by mechanical di- 

 vision. 



DISINTEGRATION. The separation of 

 a body into its integrant parts by 

 mechanical division ; the wearing 

 down of rocks ; utter separation of 

 particles. 



DISK. See Disc. 



DISLOCATION, (dislocation, Fr. dislo- 

 gazione, It.) The state of being 

 displaced; displacement of portions 

 of the earth's crust. According to 

 the theory of M. De Beaumont, the 

 principal dislocations of the earth's 



