﻿192 H. S. Williamx — Lamellibranchiata and Species-making. 



of the substance quenched. These therefore are alone avail- 

 able for the nice descriptions of strain and for the interpreta- 

 tion of what we called elsewhere the individuality of magnets. 



With the above pages we have pursued the analogy between 

 the optical behavior of tempered glass and the electrical be- 

 havior of tempered steel into every detail of consideration 

 which urged itself. We availed ourselves moreover of addi- 

 tional criteria given by the density relations of the whole or of 

 similar parts of the bodies quenched. At every stage of our 

 work we reached data alike in character both for steel and for 

 glass. With these results we are justified in maintaining that 

 sudden cooling of steel is accompanied by a strain-effect of a 

 distinct and individual kind and of an intensity sufficient to 

 account for the electrical properties of steel (thermo-electric 

 and resistance constants) such as we have found them. 



In one of the earlier paragraphs of the present paper we 

 pointed out that in its divers relations to hardness steel is dis- 

 tinguished from glass. To further our investigation it will 

 therefore next be necessary to inquire more specifically into the 

 causes of hardness itself, and therewithal to endeavor to throw 

 light on the mysterious transformations of carbon. 



Washington — Prague, June, 1886. 



Art. XX. — Devonian Lamellibranchiata and Species -making ; 

 by Henry S. Williams. 



The second portion of Professor James Hall's monograph* 

 on Devonian Lamellibranchs has been recently published, thus 

 completing volume v, Part I, of the Palaeontology of New 

 York. The first portion was devoted to the Monomyaria. 

 This second volume is devoted to the Dimyaria, is dated 1885, 

 contains pages i to lxii, and 269 to 562, and plates xxxiv 

 to xcvi with interleaved explanation of plates. The number 

 of species described is 284, which are referred to 47 genera. 

 Nine new genera are described ; Euthydesma (type, Aslarte sub- 

 textile Hall), Sphenotus (typical species, Sanguinolites arcafor- 

 mis Hall, and Cypricardia contracta Hall), Spathella (type, 

 Spathella typica Hall), Olyptocardia (type, Venericardium retros- 

 triatum von Buch, Cardium palmatum Goldfuss, Avicula speci- 

 osa Hall), Pararca, (types, Pararca venusla Hall, and Pararca 

 erecta Hall), Prorhynchus (type, Palceanatina quadrata Hall), 



* Palaeontology, vol. v, Part I, Lamellibranchiata II. text and plates. Contain- 

 ing descriptions and figures of the Dimyaria of the Upper Helderberg, Hamilton, 

 Portage and Chemung groups; by James Hall, State Geologist. Albany, 1885. 



