362 Annals of the Carnegie Museum. 



19116. ORTMANN, A. E. Monograph of the Najades of Pennsylvania. I. Ana- 

 tomical Introduction. The System of the North American Najades 

 (Mem. Carnegie Mus., 4, pp. 279-347, 4 plates). 



191 ic. Ortmann, A. E. The Classification of European Najades (Nautilus, 25, 

 pp. 5-7, 20-23). 



1908. Pilsbry, H. A. and Frierson, L. S. Description of a Mexican Lampsilis 



(Nautilus, 22, pp. 81-82). 



1909. Pilsbry, H. A. Unionidae from the Panuco River system, Mexico (Pr. Ac. 



Nat. Sci. Philadelphia, pp. 532-539). 

 1889. Schierholz, C. Ueber Entwicklung der Unioniden (Denkschr. kais. Akad. 



Wiss. Wien. Math.- naturw. CI. 55. pp. 183 ff.). 

 1892. Simpson, C. T. Notes on the Unionidae of Florida and the Southeastern 



States (Pr. U. S. Mus., 15, pp. 405-436). 

 1898. Simpson, C. T., in Baker, see Baker, F. C. 



1900a. Simpson, C. T. New and Unfigured Unionidae (Pr. Acad. Nat. Sci. Phila- 

 delphia, 52, pp. 74-86). 

 1900&. Simpson, C. T. Synopsis of the Najades, or Pearly Freshwater-mussels 



(Pr. U. S. Mus. 22, pp. 501-1044). 

 1898. Sterki, V. Some Observations on the Genital Organs of Unionidae, with 



Reference to Classification (Nautilus, 12, pp. 18-32). 

 1903. Sterki, V. Notes on the Unionidae and their Classification (Americ. 



Natural., 37, pp. 103-113). 

 1907. Sterki, V. (Note on Tritogonia tuberculata.) (Nautilus, 21, p. 48.) 



1909. Thiele, J. Mollusca, in Brauer, Die Suesswasserfauna Deutschlands, 



Heft 19, pp. 1-46. 



1910. Vanatta, E. G. Unionidae from Southeastern Arkansas and Northeastern 



Louisiana (Nautilus, 23, pp. 102-104). 

 1855. Wahl, E. von. Die Suesswasser-Bivalven Livlands (Arch. Naturk. Liv., 



Ehst- und Kurlands., ser. 2, vol. 1, pp. 75 ff.). 

 1910a. Walker, B. The Distribution of Margaritana margaritifera in North 



America (Pr. Malacol. Soc, 9). 

 19106. Walker, B. On the validity of Unio undatus Barnes (Nautilus, 24, pp. 



6-10, 16-24). 

 1910c. Walker, B. Notes on Truncilla, with a Key to the Species (Nautilus, 24, 



pp. 75-81). 



Explanation of Plate XVIII. 



Anatomy of Najades: sections of gills. 



Photographed with Bausch & Lomb Objective, 32 mm. 



Fig. 1. Quadrula lachrymosa (Lea). Sterile female. — Ohio River, St. Marys, 

 Pleasants Co., W. Va., coll. Sept. 20, 1910. — Cam. Mus., No. 61, 4,541. Horizontal 

 cross section through left inner (?) and outer (o) gill, showing marsupial structure 

 in both gills. 



Fig. 2. Pleurobcma riddelli (Lea). Sterile female. —Pearl River, Jackson, 

 Hinds Co., Miss., A. A. Hinkley coll., Nov. 5, 1910. — Carn. Mus., No. 61, 4,963. 

 Horizontal cross section through left inner (i) and outer (o) gill, showing marsupial 

 structure only in outer gill. 



