Lower Helderberg Fauna. 301 



which is destitute of an epitheca and covered by sublamellar 

 costae."* The statement that S. corniculum, whether from the 

 Trenton or Hudson Kiver Group, lacks an epitheca, is incorrect 

 (KoMiNGEE, loo. cit). The best usagef at present regards Strepte- 

 LASMA as a subgenus of Zaphrbntis. The two groups pass into 

 each other by insensible gradations, but typical forms differ in 

 this, that Streptelasma has a less complete development of dis- 

 sepimental tissue. 



Since the genus S repielasma is in honorable usage as repre- 

 senting an actual coralline type, it seems inexpedient to abandon 

 it at present in view of our inadequate knowledge of S. expansum. 

 Should a careful investigation of this species show that it does 

 not belong to the Streptelasma type, MtiTRioPHYLLOM, Edwards 

 and Haime, will probably have to be substituted. Metriophtllum 

 (type M. Boucliardi) is one of the new genera published by 

 Edwards and Haime in 1850, four years after Streptelasma was 

 established. The original description (Brit. Foss. Corals, p. Ixix) 

 is elaborated as follows : Corallum simple, turbinate, subpedicil- 

 late, inclosed in a complete epitheca. Septa appear as well- 

 developed partitions, slightly curved, and extending for the 

 most part to the center of the visceral cavity ; they are grouped, 

 in four bundles, but the cross formed by the four principal septa, 

 as it exists in other genera of the family, is indistinguishable. 

 Tabulae well developed, simple and horizontal, corresponding in 

 the different interseptal loculi in such a way as to form complete 

 transverse floors, which are usually marked by the septa, but 

 which show plainly when the latter are partially destroyed.:}: The 

 figures of M. Bouchardi and the description above quoted 

 correspond with Streptelasma. The only questionable point of 

 identity consists in the regularity of the tabulae, which in the cut 

 is so marked as to appear almost diagrammatic. The figure 

 shows that M, Bouchardi also had a central axis like a columella. 

 Although no specimens of Metriophtllum have been obtainable, 

 I have ventured to regard it as a synonym of Streptelasma. 

 Zittel, however, recognizes both genera, possibly because of their 



* Edwards and Hauie, 1850. Brit. Foss. Corals, p. Ixviii. The same idea Is repeated Mon. des Polyp. 

 Foss. des Terr. Pal., p. 393. 1851. 



^■ Hall, 1887. Pal. New York, vol. VI, p. xi, " Streptelasma," also RomNGER, loe. cit., p. 141. 



* Edwards and Haime, 1851, Mon. des Polyp. Foss. des Terr. Pal., p. 317 et seq., PI. 7, figd. 1, la, lb, 

 2,2a. 



