CONCLUDING SYNOPTICAL OBSERVATIONS. 229 



to the Scabra and Quadrata, T. Tkoracica, Mor. {' Synopsis/ pi. xv, fig. 13), from the State 

 of New Jersey and from Alabama, is allied to the AUformis group. To the same group is 

 also allied a large and abundant Mexican species, T. plicato-costata, figured and 

 described by Nyst and Galeotti ('Bull. I'Acad. de Bruxelles,' tom. vii, No. 10), from 

 the great principal Cordillera of Anahauc, Mexico, several thousands of feet above the 

 sea. This species, which was erroneously referred by the authors to the Jurassic rocks, 

 has a near ally in our T. scabricola. T. Humboldtii, von Bach (' Petref. Americ.,' 

 figs. 29, 30), another of the Scabra, has radiating costella) passing from the umbones 

 retrally over the upper and siphonal half of the shell ; its locality is San Felipe, Central 

 America. 



In the elevated region of equatorial South America, in New Granada and Columbia, 

 the same groups are represented by several unusually large and remarkable species. 

 T. ahrupta, von Buch (' Petref. Amer.,' fig. 21), an ovately oblong form, with numerous 

 delicate, almost evanescent, straight, oblique, retral or nearly perpendicular, minutely 

 crenulated costae ; the area and escutcheon, which have considerable breadth, are almost 

 plain. Also a large species named T. aliformis, by von Buch ('Petref. Amer.,' fig. 10), 

 which may be a more fully developed example of 1\ thoracica, Mor. Another is 

 T. subcrenulata, d'Orb. (' Coq. Foss. de Colomb.,' pi. iv, figs. 7, 8), a remarkably inflated 

 subcrescentic shell, allied to T. crenulata. Lam., in the general features of its orna- 

 mentation, distinguished by its more inflated and lengthened form, by the small and 

 deep concavity formed by the indistinctly separated area and escutcheon, by the zigzag 

 costella3 of their transverse ornaments, and by the small, perpendicular, widely separated 

 crenulated rows of costae. Another is a gigantic example of the Quadrata from Bogota, 

 T. Hondeana, Lea, T. Boiissignaullii (d'Orbigny, ' Coquillcs fossiles de Colombie,' pi. iv, 

 figs. 1, 2), distinguished by the gigantic size, by the extreme shortness of the general 

 figure, by the few perpendicular rows of small, widely separated, crenulated costae, and by 

 the great breadth of the area and escutcheon, whose transverse, curved costella? agree 

 with the ornaments upon the other portion of the shell ; the umbones are obtuse, and the 

 borders of the valves are rounded. 



Not less distinct and well characterised are the prevailing Trigoniac of the South 

 African provinces to the eastward of the Cape of Good Hope ; these belong to two very 

 difi'erent stages of the Cretaceous formations. That of the province of Uitenhage has 

 been investigated and illustrated by Dr. Krauss, of Stuttgart, by Dr. Rubidge, 

 and Dr. Athcrstone, who assigned thcui to the Cretaceous rocks. The fossils 

 from the same beds have been examined by Mr. D. Sharpe and Professor R. Tate, 

 and the opinion of these two palaeontologists, founded upon the analogies of the 

 fossils generally, was that they were Jurassic and should be referred to the Lower Oolites. 

 In off'ering an opinion adverse to the latter conclusion, I would admit the Jurassic aspect 

 of some of the Conchifera, which, in common with certain European forms, indicate that 

 the Jurassic fades did not disappear suddenly and entirely with the close of the Jurassic 



30 



