KA1A 



NAILS. 



1 .'. 



7'tiifi /tii3ttili,tiit. 



pitrpnrtu$. 



Spiuous Shell*. 



Example, l'n(o rpinOHU (Lea). Bartram appears to bare been the 

 fint who discovered thii species. He, apparently, found it in the 

 Muuwippi. See his ' Travel.,' p. 431. 



Dr. I.ea, in hi* < Tables,' enumerate* 323 recent ipecles as admitted, 

 and 29 u unknown to him or doubtful. 



( if the nub-genus Unto 235 recent, and 20 which he has not been 

 able to admit as certain. (Kurope, Asia, Africa, North America, 

 South America, Australia. By far most Abundant iu North America.) 



MargarilatM, 20 admitted, 2 unknown. (Europe, North America, 

 Sooth America, and perhaps Africa.) 



Ihptat, 2 recent. (Asia.) 



Anodonta, 68 admitted ; 7 unknown to Lea. (Europe, Asia, Africa, 

 North America, South America, Australia.) 



Iridina, 2 recent (Africa.) 



Spatha, 6 recent (Africa, South America.) 



M. Denhsyes Oast edition of Lamarck), after reviewing the state of 

 the question, come* to the conclusion that all the various genera can- 

 not form and ought not to form more than one genus, constituting 

 singly the family of the Naiada. 



Fouil Uioida.Tk9 recent species of Unit are very numerous 

 amounting to 2iO. These are found in North and 1 South America, 

 Kurope, Africa, Asia, and Australia. The fossil species are about 60 

 They are found in the Wealden and in the Tertiarie* of India. The 

 ipeciesj of other genera have not yet been recognised in a fossil form. 



1'nio MpitWlltt, 



NAIADES. [NAIADACE.*:.] 



NAIAS, a genus of Plant* the type of the natural order \tiiadaet<r. 

 It baa imperfect solitary sheathed flowers with no perianth. The 

 I >anvn flowers consist of 1 stamen, the fertile flowers have a single 

 short stylo with two or three filiform stigmas. There is. one British 

 species. 



JV*. flrxilit has very narrow and very minutely denticulate, ternate, 

 or opposite leaves, the sheaths ciliate-dcnt icul.ito. The ovary is solitary 

 and the style is short. It has been found in but one locality, and that 

 is near Rnundstonc, Counemara, in Qalway, Ireland. 



NAIDES, a group of Abranchiate Annelida. The species have 

 the elongated body and rings less marked than in tho Kurthwnnna, 

 They live in holes which they bore in mud at the bottom of water, 

 and from which they are constantly protruding their bodies. Some 

 have black points on their hends which have been regarded as eyes. 

 To this family belong a large number of little-studied forms of very 

 minute fresh-water worms. The smaller ones are sometimes called 

 Vibrios, of which the very common Vibrio Jluvinlilit of the amateur 

 microscopist ia an example. It also appears to embrace the Stylaria 

 of Lamarck, the Proto of Oken, and the Clymene of Savigny. This 

 family would repay attentive study. 



NAILS, the appendages to the fingers and toes in human beings ami 

 the (fuailrumana, and which are homologous with the claws and hoof* 

 of the lower animals. These organs are simply an altered form of 

 the external layer or epidermis of the skin. [SKIN.] If a portion of 

 recently formed nail is placed under the microscope it is found to 

 consist almost entirely of nucleated cells, which are of precisely the 

 same character on those f Mind in the new layers of epidermal tissue. 

 In the older portions of the nail no very distinct structure can be 

 seen, but if them parts are immersed in a dilute solution of caustic 

 potash or soda, the cell* will be mode apparent. In the human being 

 the nails are produced from a fold in the true skin. This fold or 

 groove has a highly vascular surface, which is furnished with longitu- 

 dinal elevated ridges, to which blood-vessels are copiously distributed, 

 and between which the soft inner layer of the nail dips down. The 



