C. Bcw us — Effect of Pressure on Conductivity, etc. 219 



volutions. Shell in the principal genera impunctate. Including 

 the genera : Koninckinct, JToninckeUct, Amphiclinct, Keiy- 

 seriet, f Thecosjpira, f Anoplothecct. 



Yale University Museum, May 22, 1890. 



EXPLANATION OF PLATE II, 

 Ajiphiclina dtjbia Miinster, sp. 



Figure L. — Ventral view of translucent specimen, showing attachments of prin- 

 cipal lainella? to hinge plate and spiral coils. On left side, prim- 

 ary and secondary lamellae have become separated, making double 

 spiral, x 6. 



Figure 2. — Dorsal view, showing nepionic dorsal valve, dorsal callosity, and 

 hinge area, deltidium and pedicle perforation of ventral valve, 

 x 6. 



Koninokina Leonhabdi Wissmann, sp. 



Figure 3. — Cardinal view of portion of young specimen, showing nepionic con- 

 vex dorsal shell, dorsal callosity, area, and characters of ventral 

 beak, x 18. 



Figure 4. — Similar specimen, showing slightly different features, x 18. 



Figure 5. — Dorsal view of bases of the two primary lamella? I. with loop, x 6. 



Figure 6. — Transverse section through a shell retaining both valves in position, 

 showing cross sections of the lamella? of spiral ribbon. The con- 

 tinuous and separate character of the primary and secondary 

 lamella?, and their inclination to each other, are well represented, 

 x 6 



Figure 7. — Posterior view of interior of dorsal valve showing teeth sockets, b, 

 cardinal processes, j, adductor muscular scars, a, main trunk of 

 vascular impressions, v, septum, ,s\ indentation or articulating sur- 

 face supporting dorsal edge of loop, x. x 6. 



Figure 8. — Ventral view, showing form and attachments of spiral coils. The 

 portion of loop and primary lamella? (/) concealed by secondary 

 lamella? (I') are represented by dotted lines. x 6. 



Figure 9. — Cardinal view of coils with ventral side uppeimost. showing supports 

 and attachment of primary lamella?. Secondary lamella? are rep- 

 resented by heavy black lines, x 6. 



Figure 10. — Dorsal view of young translucent specimen, showing form of spirals 

 at this stage of growth, x 6. 

 The specimens figured are in the Yale University Museum, and are all from the 



Upper Trias, of St. Cassian. 



Art. XXVII. — The effect of pressure on the electrical conduc- 

 tivity of liquids ; by C. Barus. 



1. By subjecting commercial mercury to pressures between 

 10 atm. and 400 atm.,isothermally,I found -dP/P=30xlQ- 6 

 dP, where — dP/P is the decrement of the specific electrical 

 resistance P, corresponding to the pressure increment dP. 

 If v is the symbol of volume, then from results of Grassi and 

 others,* -dv/v = SXlO~ 6 dP. Hence dP/P=10 dv/v. 



* By using the later results of Amaury and Descamps, Amagat, Tait, I should 

 not materially change the remarks of the text. 



