168 ME, J. W. GREGOET ON ARCH^OPNEXTSTES ABRTJPTUS. 



III. Geological Evidence. 



But, in ad Htion to the biological value of Archceopneustes ahruptus, 

 it is of interest as throwing further light on the relations of the Eadio- 

 larian Series of Barbados. We have seen that its closest allies are 

 two species now living in the West Indies and two extinct species 

 from Cuba. The last had been assigned to the Cretaceous by 

 MM. d'Orbigny and Cotteau, owing to their resemblance to the 

 common Chalk Ecliinocorys. The discovery, however, of some frag- 

 ments of one of the species (A. cuhenslfi) in some beds in the island 

 of St. Bartholomew referred to the Eocene, led M. Cotteau ^ to regard 

 the Cuban deposits as also of this age. Subsequent authorities 

 have still further raised the horizon in the geological scale. Thus 

 Prof, von Zittel ^ places the genus as Miocene, while Sr. M. F. de 

 Castro ^ puts it as Miocene or Pliocene. But the specimens from 

 St. Bartholomew being mere fragments, perhaps no especial value need 

 be attached to them. As A. abruptus and A. cuhensis are both fairly 

 closely allied to A. hystrioc, one would be inclined, in the absence of 

 other evidence, to follow Sr. de Castro and simply call them Upper 

 Cainozoic. To whatever age the Eadiolarian Series be ultimately 

 referred, the Cuban beds will probably also be found to belong to 

 the same period ; the lithological condition of the Echinoids in the 

 two islands seems identical. 



Prof. W. Dames has described an Oligocene (Aquitanian) species 

 which he referred to Paloeopneustes ; but, as the anterior ambulacrum 

 is well developed, it must belong to another genus, as Duncan had 

 already pointed out. 



In regard to the depth of the deposit, A. hystrioo ranges down to 

 a depth of 208 fathoms; it is thus not a deep-sea species, nor, even 

 in the absence of any such data, would one be likely to regard this 

 thickly plated A. abruptus as an abyssal form. The specimen was 

 found on Bissex Hill, towards the top of the Oceanic Series ; it is 

 from the same horizon as some Echiuoid spines, fish- teeth, simple 

 corals (as yet undetermined), and a few mollusca : the horizon is 

 towards the top of the series, but, as Bissex Hill is an outlier, its 

 exact position is as yet undetermined.'* The characters both of the 

 Echinoid and its matrix are quite different from those of the deep-sea 

 Cystechinvs crassus,^ Creg., from another part of the series. Archceo- 

 pneustes cibruptus seems to have lived after the close of the period 

 of maximum depression, and the band of limestone nodules in which 



^ ' Description des Echinides Tertiairea des lies St.-Barthelemy et Anguilla/ 

 Handl. k. Svenska Vetensk. Akad. Bd. xiii. no. 6 (1875), p. 46. 



2 ' Handbuch der Palaontologie,' Bd. i. (Miinchen, 1879) p. 536. 



^ ' Pruebas Paleontologieas de que la Isla de Cuba ha estado unida al con- 

 tinente Americano, y breve idea de sii constitucion geologica,' Bol. Com. Mapa 

 geol. Espafia, t. viii. (1881) p. 364. 



* For the geologjv of the locality, see J. B. Harrison and A. J. Jukes-Browne, 

 ' The Geology of B'arbados,' Salisbury (1890), pp. 24, 25. 



^ J.W.Gregory, ' Cystechimcs crassics, a new species from the Eadiolarian 

 Marls of Barbados, and the evidence it affords as to the age and origin of those 

 deposits,' Quart. Journ. Geol. Soc. vol. xlv. (1889) pp. 61U-650. 



