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NUT 



of Mr. S. Woodward, if a line be drawn 

 from Cromer, on the northern coast of 

 Norfolk, to Wayburn, about six miles 

 west, and from thence extending in a 

 southerly direction towards Norwich, 

 about 18 miles, it will comprise all the 

 regular beds of Norfolk crag. 



NOVA'CULITE. (from novacula, a razor, 

 Lat.) The Wetz schiefer of Werner ; ar- 

 gile schisteuse novaculaire of Haiiy. Hone- 

 stone. See Hone. 



NU'CLEUS. (nucletis, a kernel, Lat.) A 

 solid centre or point, round which matter 

 is collected. 



NU'CULA. A genus of marine bivalve shells 

 belonging to the family Arcacea. An 

 inequilateral, equivalved, transverse, sub- 

 trigonal bivalve ; covered with an epi- 

 dermis. The hinge linear, bent at an 

 angle formed by numerous, alternately 

 inserted teeth ; muscular impressions, 

 two, simple ; beaks approximating, and 

 turned backwards. The recent species of 

 this genus are found in estuaries, and in 

 the ocean, at depths varying to sixty fa- 

 thoms, in mud and sand. 



Of fossil species, one is mentioned by 

 Dr. Mantell, as found in the upper green - 

 sand, and one in the lower green- sand. 

 Mr. Parkinson states that he has found 

 shells of the Nucula inargaritaeea, with 

 their fine comb-like teeth, and their pearly 

 coat, quite perfect, in the Essex bank of 

 shells ; and in a perfect state, and of a 

 microscopic size, at Plumsted ; also some 

 minute calcedonvc specimens, in a perfect 

 state, from the Devonshire whetstone. 

 Several species are described by La- 

 marck. 



NU'DIBRANCHIATA. The second order of 

 the class Gasteropoda. The nudibran- 

 cliiata have no shell whatever ; neither 

 are they furnished with any pulmonary 

 cavity, their branchiae being exposed on 

 some part of their back, from which cir- 

 cumstance they have obtained their name. 

 The triton, doris, &c. are examples. 



NU'MMULITE. (from nummus, money, Lat. 

 and Xi0oc, a stone, Gr.) The nummu- 

 lites compose a fossil extinct genus of mul- 

 tilocular cephalopods, presenting, exter- 

 nally, a lenticular figure, without any 

 apparent opening, and, internally, a 

 spiral cavity, divided by septa into nu- 

 merous chambers ; they do not possess a 

 siphuncle, but their chambers communi- 

 cate by means of small foramina with each 

 other. They have obtained their name 

 from their supposed resemblance to pieces 

 of money. It is of stone composed of 

 Nummulites that the pyramids of Egypt 

 are constructed. The extreme obscurity 

 in which the nature of nummulites has 

 been involved, almost to the present day, 

 has occasioned the adoption of various 



vague and absurd notions respecting their 

 origin, and a variety of names have been 

 assigned to them. Thus, they have been 

 named Helicites, from their spiral struc- 

 ture ; Phacites, from their resemblance 

 to a lentil ; and Salicites, from the sup- 

 posed resemblance of their sections to 

 the leaf of the willow. Pliny is supposed 

 to refer to them, under the name of Daph- 

 nias. when he mentions that Zoroaster em- 

 ployed these substances for the cure of 

 epilepsy. They have been also termed 

 Lentes lapidea?, Lapides cumini, circu- 

 lares, numismales, &c. 



Scheuchzer was the first who concluded 

 that these bodies ought to be ranked 

 among the mineralized remains of animals 

 which had lived before the flood. 



Nummulites vary in size from less than 

 an eighth of an inch, or even microscopic 

 minuteness, to an inch and a half in dia- 

 meter. Their surface is in some nearly 

 smooth, in others rough and scabrous, 

 with numerous small projecting knobs, or 

 undulating lines. Their colour varies 

 from nearly white to brown and red, and 

 sometimes nearly blue. The number of 

 spiral turns seems to depend on the age 

 and size of the animal : in those of a 

 quarter of an inch in diameter, being 

 three or four, while in those of the largest 

 size the number of whorls is frequently 

 upwards of twenty. Lamarck divides the 

 genus into four species. 



Nummulites occupy an important place 

 in the history of fossil shells, on account 

 of the prodigious extent to which they are 

 accumulated in the later members of the 

 secondary, and in many of the tertiary 

 strata.' They are often piled on each other 

 nearly in as close contact as the grains in 

 a heap of corn. Entire calcareous hills 

 are composed of fossil nummulites. 



NUMMULI'TIC. Containing nummulites ; 

 composed of nummulites. 



NU'TANT. (from nutans, nodding, Lat.) 

 A perpendicular part, the apex of which 

 bends over. 



NUTA'TION. (from nutatio, a nodding, Lat. 

 nutation, Fr.) A tremulous or vibratory 

 motion of the earth's axis, by which its 

 inclination to the plane of the ecliptic is 

 continually varying, being, in its annual 

 revolution, twice inclined to the ecliptic, 

 and as often returning to its former po- 

 sition. Both the celestial latitudes and 

 longitudes are altered to a small degree by 

 nutation. In consequence of this real 

 motion in the earth's axis, the pole-star, 

 forming part of the constellation of the 

 Little Bear, which was formerly 12 from 

 the celestial pole, is now within 1 24' of 

 it, and will continue to approach it till it 

 is within i, after which it will retreat 

 from the pole for ages ; and 12,934 years 



