SYNOPSIS OF THE NAIADES— SIMPSOK. 677 



t Alasmodon falcata Gould, Pr. Boston Soc. Nat. Hist., Ill, 1850, p. 294; * Otia 

 Couch., 1862, 1). 87;'—" U. S. Expl. Exp., XII, 18.52, p. 433, figs. 545, 54.5«, 

 545^.— CoNKAD, Pr. Ac. Nilt. Bci. Phila., VI, 1853, p. 262.— P.etel, Conch. 

 Sam., Ill, 1890, p. 173. 



^UniofalcatHs Sowekbv, Conch. Icon., XVI, 1868, pi. lxxv, fig. 390. 



*Uvio { Alasmodonta) complanaius Middendorff, Sib. Reise, 11,1851, Pt. 1, ]•. 273, 

 p!. XXVII, figs. 1-6.- 



^Marijarhana complanata Westerlund, Faun. Pal., II, Pt. 7, 1890, p. 187. 



* rulo moiKjolictts MiDDENDORFF, Sib. Keise, II, 1851, p. 277, pi. xxvii, figs. 7, 8. — 



" llKSSLiNG, Perl, und Ihi-e Perlen, 1859, p. 203. — ' Schkenck, Eeise und F. im 

 Amnr-Lande, II, 1867, p. 699.^*" Westerlund, Kong. Sv. Vet. Ak. Hand, XIV, 

 no. 12, 1876, p. 74. — "P.etkl, Conch. Sam., Ill, 1890, p. 155. — 'Westerlund, 

 Faun, der Pal., II, Pt. 7, 1890, p. 113. 



* Alasmodon yiihaensis Trask, Pr. Cal. Acad. Sci., 1, 1855, p. 30. 

 *1Margariiana rareneUaiia Chenu., Man., 1859, II, p. 144, fig. 714.' 



All Europe except the southernmost portion ; northern Asiaj Japan ; 

 northern E"orth America; Iceland. Its southern limit seems to be 

 about north latitude 40°. It apjiears to be entirely circumboreal, except 

 that, so far as is known, it is missing in the central part of the ]Srorth 

 American continent. Wetherby has suggested that it may have been 

 destroyed in this region by the ice of the glacial epoch. It is found in 

 the upjjer Missouri and in Canada East, New York, and the New Eng- 

 land States. 



t MARGARITANA CRASSA Retzius. 



^Mya testa crassa, Scuroter, Flussconch., 1779, p. 182, pi. ii, tig. 2. 



* Unio crasaus Retzius, Diss. Hist. Nat., 1778, p. 17.^ — Spengler, Skriv. Nat. Selsk., 



Ill, 1793, p. 56.— " ScHOLZ, Schleis., L. nnd W. Moll., 1843, p. 130.— * von 

 Wahl, Arch. Natnrkunde Liv., 2d. ser., I, 1855, p. 94. — * H. and A. Adams, 

 Gen. Rec. Moll., II, 1857, p. 491.— *Drouet, Moll. Cote d'Or., 1867, p. 101.— 

 * Jordan, Jahrb. Dentsch. Mai. Ges., VI, 1879, p. 306.—* Drouet, Mem. Acad. 

 Dijon, 3d ser., VII, 1882, p. 13."'— "PzETEL, Conch. Sam., Ill, 1890, p. 149. 



' This is undoubtedly ?Ha)'$frtri/(/'errt, but in the types the young shells show laterals. 



■^ I have no doubt that this is Manjaritana margaritifera L. and not Unio complanatus 

 Solander as Middeudorff supposes. The specimens figured are terribly eroded, and 

 the hinges are in very bad order, but they do not show laterals. 



3 Numerous varieties as well as species have been made of this abundant, wide- 

 spread form. Notwithstanding its enormous distribution, the widest of any Naiad 

 known, I have seen no A^ariatiou that seems to me to be worthy of a varietal name. 



^ Retzius' description is in Latin, and consists of ten words, and as he does not 

 figure the species, it would be impossible to determine what he meant only for the 

 fact that he refers to the Flussconchylien of Schroter {Mya testa crassa, p. 182, pi. ii, 

 tig. 2). Schroter's figure is not a very good one, but I can have no doubt that he had 

 before him the large, heavy, black Naiad, with lateral teeth, found in southern Europe. 

 In general it closely resembles the M. margaritifera externally, but the epidermis is 

 a more dull black, the beaks are usually higher and more strongly developed, the 

 nacre is white, and it has fairly well-developed laterals. European conchologists 

 seem to have quite commonlj'^ mistaken heavy, large forms of Unio hataviis for Retzius' 

 species, and in a number of cases the Al. margaritifera has been takeu for it. 



" Page 13 of reprint; I have not seen the original. 



