116 THE NAUTILUS. 



lusca of Indiana, in Indiana Dept. of Geology, 24th An- 

 nual Report, 1900, pp. 437 & sqq. (CorbiculadaB). 



CLESSIN, S., Die Familie der Cycladeen, Martini & Chemnitz, 

 Vol. 9, pt. 3, 1879. 



PELSENEER, PAUL, A Treatise on Zoology edited by E. Ray 

 Lankester, Part V Mollusca, London, 1906. 



PRIME, TEMPLE, Monograph of American Corbiculadse. Smith- 

 sonian Inst., 1865. 



STERKI, V., The Nautilus, XXV, p. 1, 1911. 



WALKER, BRYANT, On Certain Abnormal Sphaeria, The Nau- 

 tilus, IX, p. 135, 1896 ; Conf. 1. c. XII, p. 117, 1899. 



WESTERLUND, CARL AGARDH, Fauna der . . . Palaaarctischen 

 . . . Binneuconchylieu, VII, Malacozoa Acephala. 



WOODWARD, B. B., Catalogue of the British Species of Pisi- 

 dium. British Museum, 1913. 



EXPLANATION OF FIGURES, PLATE III. 



Hinges of Sphseriidaa; in all figures, the right valve is ou 

 the right, and the left on the left hand, the posterior is above, 

 the anterior below. 



Fig. 1 : lateral view of the hinge of Pisidium, diagram- 

 matic; 1, ligament; m, dorsal valve margin; p. (in figs. 9 

 and 10, periostracum ; ; shell membrane ; pi, hinge plate ; 

 u, umbones (beaks); cardinals: C3 of the right valve; C3i, 

 posterior part of the same, proper, or inner ; C3o, additional 

 or outer component; of the left valve: C2 anterior, C4 pos- 

 terior; lamina?: al anterior inner or principal, alii anterior 

 outer of the right valve ; all anterior left ; pi and pill pos- 

 terior inner and outer of the right valve, pll posterior left. 



Fig. 2 : the same, viewed from below ; notice that the cusps 

 of the left laminae are projecting over the level of the valve- 

 edges, and thus over the median or sagittal plane, and the 

 same in figs. 3 and 7 ; symbols the same as in fig. 1. 



Fig. 3 : Sphccrium solidulum Prime, viewed from below in 

 partly open (gaping) mussel. 



Figs. 4, 5, 6 to show differences in the configuration in some 

 species of Pisidium; 4, P. compressum Prime, form, half- 

 diagrammatic ; mussel about 4.5 mm. long ; the separate fig- 

 ures show cardinals somewhat in detail. 



Fig. 5, P. fabale Sterki (from Montana), about 7 mm. 

 long (the plate of the right valve is somewhat too broad). 



Fig. 6, P. vesiciilare Sterki, mussel about 2 mm. long; the 



