682 EEPORT— 1888. 



and covered with fine granulated lines crossing minute rays ; Ft. bellula, a species 

 like Pt. fasciculata, Goldf., but with few alternating ribs crossed by distant zi^zao- 

 strife ; Aviculopecten hirundella, separated from Pt. texturata by its shorter hinge 

 line and finer reticulation (the right valve has transverse marks similar to those of 

 Pt. ala. Barr.) A. avifonnis, a fiat recurved shell much produced and rounded 

 behind, with very small umbo and wings; A. coi?ima, similar to the preceding, but 

 much smaller and with reticulated surface ; A. gracillimus, a flat, elongate, sub- 

 equilateral form, with minute umbo, notched anterior ear and close alternatino- 

 ribs ; Mytillus Rohertsii, which is more ovoid and less produced in the postero- 

 superior region than M. dimidiatus, Goldf. ; M. stultus, a short, squarish form, with 

 fine concentric strife and a few stronger ones ; M. pinnoides, which is shorter and 

 has a more direct umbo than M. uncinatus, Eichw. ; Mijalina elUfticn, a smooth, 

 convex ovoid shell, differing from Unio castor, Eichw., iu its more incurved umbo, 

 and less dilate wings ; Meyalodon colmnbinus, separated from M. carinatus, Goldf., 

 by its finer, regular plaits, more terminal umbo, and the contour of its elevated 

 keel ; M. ? 2)ro7ninens, larger than the last, and with coarser wavy plaits, loftier 

 and more projecting umbo, and more oblique anterior margin ; Ctenodontn? lepida, 

 a small, flat, transverse shell, which is narrower and more convex anteriorly than 

 P. modiolaris, F. A. Pvci. ; Cardiomorpha ? poUta, a flat, oblique species, unlike A. 

 damnoniensis, Ph., in its smoothness and its shorter hmge-line ; Cypricnrdia negleda, 

 with fewer, stronger ribs and more definite wing thanM. scalaris, Ph., C. guttata, 

 with fewer plaits and rounder indentations than G. crenistria, Sandb. ; C. ensiformis, 

 a much flatter and wider shell than C. neglecta, and with more and finer plaits ; 

 Edmondia ? dubia, a large, wide convex shell, with a recurved anterior umbo, deep 

 area and close, indistinct, bifurcating growth, lines ; Hexacrinus perarmatiis, with 

 calix, like H. macrotatus, Aust., but covered with sharp, regular, non-confluent 

 tubercles ; H. microglyphkus, with a convex calix, very long basals, and fine orna- 

 mentfition ; riatycrinm aherrans, with trilobed attachment, elongate calix, three 

 squarish basal, four or five long radials, intercalated with one large and one small 

 subsidiary anal ; llaplocrinus dedpiens, a minute crinoid, having a short calix with 

 an elevated conical summit, with key-shaped grooves for the arms; IViccelocrinus? 

 Zeej^with shorter limbs and shallower excavations than T. Woodmani, Mate and 

 Worthen; and Serpula? devonica, a long, straight, smooth, and cylindrical tube. 



Sub-Section C. 



1. Mineralogical Evolution. By T. Steekt Hunt, LL.D., F.B.8. 



In a paper read by the author in 1887, before the Geological Section of the British 

 Association for the Advancement of Science, on The Elements of Primary Geology, 

 it was said that ' the transformation of the primitive igneous material of the 

 earth's crust through the action of air and water, aided by internal heat, presents 

 a mineralogical evolution not less regular, constant, and definite in its results than 

 the evolution apparent in the organic kingdoms.' '■ The details of this complex 

 evolutionary process, as explained by what the writer has named the crenitic 

 hypothesis, have been elsewhere set forth at length, on more than one occasion, and 

 involve the whole chemical history of the various mineral species which enter into 

 the constitution of rock-masses, but especially their relations to subterranean 

 changes under the influence of heated water, and to atmospheric action. As we 

 have pointed out, the transformation of basalt into the hydrous porodic body 

 known as palagonite, and the subsequent partial conversion of this into a crystal- 

 line zeolite, as described by Bunsen, furnishes a significant illustration of the 

 proce.ss under consideration. 



The stability of silicated species under atmospheric influences is very variable, 



• Transactions, p. 704 ; also Geological Magazine, November 1887. 



