Reviews — T/iomas 8f MacA/isfcr — Ore Deposits. 565 



emphasizes the presence of both dental plates and median septum. 

 Squamidaria includes forms which appear to bear the same relation to 

 Reticularia in surface ornamentation as Athyris does to Cleiothyridina. 

 It is further distinguished from Reticularia by the absence of dental 

 plates and median septum. Gremraellaro originally established 

 Squanmlaria on certain peculiarities of the brachia and the possession 

 of tiexuous lamellose expansions externally. 



Meterelasma, a new genus of the Terebratulidge, is based on 

 peculiai'ities of internal structure. The names Leptodus, Composita, 

 and Cleiothyridina are employed in accordance with Buckman's usage 

 instead of Lyttonia, Seminula, and Cleiothyris. 



A new lamellibranch genus is described under the name Protrete. 

 It bears a certain resemblance to Pleurophorella, from which it differs 

 in having a tubular perforation under the umbones. This perforation 

 is supposed to be a real opening into tlie interior of the shell. Other 

 distinguishing features are the absence of radial ribs and papilliB. 

 The general shape suggests Lithodomiis, but the possession of the 

 anterior opening distinguishes it from this as well as other genera 

 which it outwardly approaches. 



Peritrochia is a new Cephalopod belonging to the Pronoritidae. 

 " The most closely related genus is Pronorites. The suture of 

 Pronorites is almost exactly that of Peritrochia^ save that there is 

 a tendency in the lobes toward a pointed, linguiform shape. The 

 shape of the shell in Pronorites, however, is discoidal and the whorl 

 section elongate and subquadrate, while the shell in Peritrochia is 

 globose and the whorl section transverse and lunate. The umbilicus 

 in one is wide and in the other closed." 



Finally a new trilobite genus, Anisopyge, is described as belonging 

 to tlie Proetidse. It comes nearest to Phillipsia, but differs from that 

 genus as typically found, in having a more pyriform glabella, smaller 

 fixed cheeks, and also in other respects. One of the most marked 

 features, however, is the presence in Anisopyge of thirty pygidial 

 segments together with "a very striking discrepancy between the 

 segments of the axis and those of the pleural regions, a discrepancy 

 emphasized by the presence of an unsegmented band along either side 

 of the axis ". 



Tliirty-one excellent plates illustrate this valuable monograph. 



IvoK Thomas. 



IV. — The Geology of Ore Deposits. By H. H. Thomas, M.A., B.Sc, 

 and D. A. MacAlistek, Assoc. R.S.M. Illustrated. Crown 8vo ; 

 pp. xi and 416. London: Edward Arnold. Price 7«. 6(^. net. 



rnmS work is the second of a series to be published under the 

 X editorship of Professor J. E. Marr, and intended chiefly for 

 students of economic geology, but also for students of general geology, 

 miners, surveyors, and others who are concerned with the practical 

 applications of the science. To those who are familiar with ore 

 deposits, the task of catering for such a wide range of readers within 

 the limits of one small volume appears tremendous, and our heartiest 



