SYNOPSIS OF THE NAIADES SIMPSON. 677 



t Alannwdon falcata GOI:M>, Pr. Boston Sue. Nat. Hist., Ill, 1850, p. 294; * Otia 

 Conch., 1X112, n. 87;'' U. S. Expl. Exp., XII, 1852, p. 438, figs. 545, 545a, 

 515ft. CONRAD, Pr. Ac. Nat. Sci. Phila., VI, 1853, p. 2<>2. P.KTEL, Couch. 

 Sam., Ill, 1890, p. 173. 

 *Uniofalcatits SOWERHY, Conch. Icou., XVI, 1868, pi. i,xxv, tig. 390. 



* I'nlo ( Alasmodonta) complanatns MIDDENDORKK, Sib. Reise, 11,1851, Pt. 1, p. 273, 



pi. xxvii, figs. 1-6.- 



*Mary<trUuna complanatti WKSTERLUND, Faun. Pal., II, Pt. 7, 1890, p. 187. 

 1'nio iHon;/olicH8 MIDDKXDORKF, Sib. Reise, II, 1851, p. 277, pi. xxvii, figs. 7, 8. 

 " HKSSLING, Perl, und Hire Perlcn, 1859, p. 203. * SCIIKENCK, Reisc und F. iin 

 Amiir-Lande, II, 1867, p. 699.* WESTERLUXD, Kong. Sv. Vet. Ak. Hand, XIV, 

 no. 12. 1876, p. 74." P.KTKL, Conch. Sam., Ill, 1890, p. 159. * WESTKRLUND, 

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



*Alaxiodii ynbaeiisis TRASK, Pr. Cal. Acad. Sci., 1, 1855, p. 30. 



*1Margaritana ranmelidiia CIIENU., Man., 1859, II, p. 144, fig. 714. :1 



All Europe except the southernmost portion ; northern Asia; Japan ; 

 northern North America; Iceland. Its southern limit seems to be 

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

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

 American continent. Wetherby has suggested that it may have been 

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

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

 land States. 



fMARGARITANA CRASSA Retzius. 



*Mya testa crasm, SCHROTEK, Flusscoiich., 1779, p. 182, pi. u, fig. 2. 



* Unio craxstts RETZIUS, Diss. Hist. Nat., 1778, p. 17. 4 SPENGI.KR, Skriv. Nat. Selsk., 



Ill, 1793, p. 56. * SCIIOL/,, Schleis., L. und. W. Moll., 1843, p. 130. * VON 

 WAHL, Arch. Naturkunde Liv., 2d. ser., I, 1855, p. 94. * H. and A. ADAMS, 

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

 * JORDAX, Jahrb. Deutsch. Mai. Ges., VI, 1879, p. 306. * DROUET, Mem. Acad. 

 1 )ijou, 3d ser;, VII, 1882, p. 13. * P^TKL, Coneh..Sain., Ill, 1890, p. 149. 



1 This is undoubtedly margaritifera, but in the types the young shells show laterals. 



- 1 have no doubt that this is Maryaritana margaritifera TJ. and not Unio complanatus 

 Solander as Middendorft" 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 variation that seems to me to be worthy of a varietal name. 



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

 figure the species, it would bo impossible to determine what ho meant only for the 

 fact that he refers to the Flussconchylieu of Sch niter (lfj/a testa crassa, p. 182, pi. n, 

 fig. 2). Schroter's figure is not a very good one, but I can have uo 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. maryaritifera 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 commonly mistaken heavy, large forms of Un io lataviis for Ret/ins' 

 species, and in a number of cases the M. mar gar it \fcra has been taken for it. 



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



