C. D. Walcott — Archeocyathus of Billings. 145 



in each case, an abundance of opaque and transparent octahe- 

 dral crystals. Nevertheless certain mineralogical differences 

 are apparent. The pyrope with its alteration rim, described by 

 Mr. Diller, is wanting in the Syracuse rock ; ilmenite too, 

 estimated to compose 2*2 per cent of the Kentucky peridotite, 

 was not detected in the Syracuse occurrence. On the other 

 hand, biotite and enstatite are much more important constituents 

 in the latter than in the former. The little transparent crystals 

 in the Kentucky peridotite are considered by Mr. Diller, as 

 anatase (octahedrite) which has resulted from the alteration of 

 the ilmenite. For reasons above stated, those in the Syracuse 

 rock must, however, be regarded as perofskite, although their 

 resemblance is so great as to suggest that they are the same 

 mineral in both cases. 



Petrographical Laboratory of Johns Hopkins University, Baltimore, April, 1887. 

 ■» 



Art. XVIII. — Note on the Genus Archeocyathus of Billings ; by 

 Charles D. Walcott. 



The genus Archeocyathus was proposed by Mr. E. Billings, 

 in a pamphlet entitled " Geological Survey of Canada : Sir W. 

 E. Logan, Director. ' New Species of Lower Silurian Fossils ;' 

 by E. Billings, F.G.S., Paleontologist G.S.C. Montreal, 21st 

 November, 1861." 



A copy of this pamphlet was received by Professor Jules 

 Marcou on December 15th, 1861. 



In a copy of the pamphlet now before me the genus is 

 described on page 3, and the characters are largely drawn from 

 A. Atlanticus, the first species following the generic description 

 on page 4. The second species is A. Minganensis, a form 

 referred to the genus, not used as its type, and it was not illus- 

 trated. In 1865 Mr. Billings proposed the species Archeocya- 

 thus profundus (Pal. Foss., vol. i, p. 4), and placed it after the 

 description of the genus, without mentioning that the genus 

 was founded on A. Atlanticus, and, on p. 355, he gives A. pro- 

 fundus as the type, then A. Minganensis ; and refers to A. 

 Atlanticus as the third species of the genus. This has led 

 the paleontologists, who have not seen the pamphlet of 1861, 

 to consider A. profundus as the type of the genus Archeo- 

 cyathus. 



I found that A. Atlanticus belonged to one genus and A. 



profundus to a different and distinct genus ; and as Mr. F. B. 



Meek had proposed the genus Ethmophyllum for a species 



generically identical with A. profundus, I referred the latter 



species to Ethmophyllum, as the type of a genus cannot be 



Am. Jour. Sci — Third Series, Vol. XXXIV, No. 200.— August, 1887. 

 10 



