158 CATALOGUE OF THE BLASTOIDEA. 



Sp. Char. Calyx short, or moderately long, ovoid, round-ovoid, ovoid-oblong, or 

 ovoid-conoidal ; summit more or less truncate ; peristome usually concave ; base sub- 

 truncate or flattened, but never absolutely cut off at right angles to the vertical axis ; 

 section obtusely pentangular ; periphery sometimes at the radial lips, but more 

 commonly above them. Basal plates forming a shallow, saucer-like slightly pro- 

 tuberant cup, always more or less visible in a side view, and presenting in the middle 

 line a small papillary elevation, on which is placed the columnar facet. Eadials 

 pentagonal oblong in outline, occupying about half the length of the calyx ; bodies 

 more or less abruptly deflected inwards and downwards, and obliquely subangulur in 

 the middle line; limbs narrow, with rather steep sides ; sinuses broad and deep, with 

 sharp prominent margins ; lips quite simple ; interradial sutures in concavities. 

 Deltoid-plates rhombic-lanceolate, sharp edged, and concave, their external apices 

 not reaching the summit. Ambulacra more or less concave ; lancet-plates take up 

 about half their entire widtli ; ambulacral groove wide, shallow, and straight, 

 the lateral grooves almost at right angles to the main groove ; side plates oblong, 

 thirty to forty ; outer side plates very small ; pores elongately pyriform. Hydro- 

 spire-folds four or five (? sometimes three) on each side of an ambulacrum, and 

 always closely approximated beneath it. Spiracles triangular-ovate, the septa short 

 and confined to the outer ends of the openings; the anal spiracle usually with a 

 more elevated outer edge than the others. Mouth moderately large. Ornament 

 seldom preserved. 



EcmarJcs. Pentremitcs Godoni, or as it has been more frequently, though incorrectly, 

 called P.florealis, appears to have been universally accepted as the type, not only of 

 the genus Pentremites, but also of the entire group Blastoidea. According to the 

 ordinary rules of nomenclature, P. globosa, Say, should be considered as such because 

 it was the first species described by Say. So much difference of opinion, however, 

 appears to exist as to what is P. globosa, Say, that we think it would much simplify 

 matters were this name totally expunged l . The species next described, P. jiyriformis. 

 Say, should take its place, and although this would be the correct course to pursue, 

 we hesitate to displace P. Godoni from a position so long occupied by it with 

 advantage. 



Either Shumard or Hall appears to have been the first to refer to this species in 

 1858 under its true name, P. Godoni, Defr., sp. In fact with the exception of 

 Messrs. Lyon and Casscday, they were the only authors who used this name, until a 

 comparatively recent period. P. Godoni is very abundant, and is to be met with 

 in all collections. Say says, " Near Huntsville they are very numerous, and on 

 the surface of a fragment of rock, three inches long by two and a quarter wide, . . . 



1 If the specimen -which Say described by this name really came from the neighbourhood of Eath, it is 

 not improbably our Acentrotremites ellipticus (PL XIII. figs. 17, 18), which occurs in the Carboniferous 

 Limestone of Somersetshire. 



