DESCRIPTIONS OF THE SPECIES. 169 



Mountain, Tennessee; Huntsville, Alabama; and Alleghany Mountains: Chester 

 group, Subcarboniferoiis. 



Genus PENTKEMITTDEA, SOrMgny, 1849 {emend. E. & C. 1882). 



Pentremilidea, d'Orb. (pars), Trod. Pal. Stmt. 1SI!>, tome i. p. 102. 



Pentremitidea, d'Orb. (pars), Coura element. Pal. et Geol. L852, tome ii. fa*. 1. p. 139. 



Pentatrematites Truncati, Roemer (pars), Archiv I'. Naturgesch. 1851, Jahrg. xvii. Bd. L. 



p. 3G8. 

 Pentremites, Schultzc, Denkschr. k. Akad. Wissensch. Wien, 18G7, Bd. xxvi. Abth. 2, 



p. 223. 

 Pentremitidea (pars), E. & C, Ann. & Mag. Nat. Hist. 1882, vol. ix. p. 220. 



Gen. Char. Calyx varying in outline from elongately clavate-pyramidal to penta- 

 gonal-obpyriform ; summit truncate or convex ; base usually long and conical. 

 Number and disposition of the plates as in Pentremites proper, but the deltoids 

 are inconspicuous, generally confined to the summit, and rarely visible in a side view. 

 Basal plates convex, forming a more or less high cup, and frequently carinate. 

 Radial plates always strongly lobate. Ambulacra narrow, and usually not greatly 

 depressed within the radial sinuses ; side plates lying on the lancet-plates so as to 

 conceal them more or less completely. Spiracles usually large, and constructed 

 like those of Pentremites, as are also the hydrospires. Anus confluent with the two 

 spiracles at its sides to form a common anal spiracle ; the anal deltoid plate some- 

 times rather larger than the others. 



History and Remarks. The name Pentremitidea was proposed by M. Alcide 

 d'Orbigny in 1849 for two Devonian Blastoids from Spain, which he believed to be 

 peculiar in having a calyx composed of but two rows of plates, the basals and the 

 radials. lloemer showed l , however, that the two species in question — Pentremitidea 

 Paillettei, de Verneuil, sp., and P. Schuhii, d'Arch. & de Vein., sp., are provided, like 

 other Blastoids, with the third row of calyx-plates or deltoids. On these grounds, 

 therefore, Pentremitidea has not been adopted by later writers on this interesting 

 class. It appears, however, that P. Paillettei, in common with a considerable number 

 of other forms, possesses peculiarities of calycnlar structure which separate it at once 

 from Pentremites, as understood by us. We have in consequence rehabilitated 

 d'Orbigny's name for such species, although it might be contended by some that an 

 entirely new name would have been preferable in this case. We are therefore glad 

 to find that our view has been accepted by such authorities as Messrs. Wachsmuth 

 and Barris 2 . 



The calyx of Pentremitidea is either more slender and elongate than that of 



1 Archiv f. Naturgesch. 1851, Jahrg. xvii. Bd. i. pp. 368, 369. 



2 Report Geol. Survey Illinois, lb83, vol. vii. p. 363 ; Troc. Daveuport Acad. Nat. Sci. 1885, vol. iv. p. 93. 



Z 



