Zooruyva. | LOWER PALAXOZOIC RADIATA. 39 
2nd Subfamily. TURBINOLIN &. 
Outer wall thin, imperforate; lamellee meeting in the centre, or joming the axis, when present, 
without the intervention of pali. 
I only know one Paleozoic genus probably referrible to this subfamily. 
Genus. PETRAIA (Miinst.) as elucidated by Lonsdale. 
= Streptolasma (Hall, 1847). 
Gen. Char.—Corallum simple, turbinate, radiating lamellee of one or two sizes, the larger extending 
from the walls to the centre where they are more or less twisted, (often thus forming a spirally rolled 
conical centre, the base upwards), without connecting vesicular plates, or transverse diaphragms. 
I find that the flattened appearance often seen truncating the apex of the commonly-seen casts of 
this genus, and which has been taken for the impression of a diaphragm, is really produced by a nearly 
solid calcareous filling up of the old apex of the cone, and which, with the rest of the coral, often 
disappears in sandy matrices. The lamellze are often perforated by long tubes opening as papille on their 
edges, as in the supposed genus 7’ryplasma (Lonsd.) An irregularity at one side, as in Caninia, is very 
common, marked by one strong plate extending directly to the centre, and several on each side uniting 
branch-wise to it; a corresponding peculiarity is seen on the external strie. The rounded ridges of 
the cast are moulded on the diverging halves of the split outer edges of the biplated lamellae which 
occupied the sulci. The genus differs from Strephodes (M*Coy) in wanting the vesicular structure between the 
lamellae, and from Calophyllwm (Dana) in the supposed want of transverse diaphragins. 
PETRAIA AQuISULCATA (J/‘°Coy). Pl. 1. B. fig. 23, and 24. 
Ref.—M Coy, Ann. Nat. Hist. 2nd Series, Vol. VI. p. 279. 
Sp. Ch—Conical, slightly curved, oblique, with a few broad, obtuse, undefined concentric swellings of 
growth, regularly increasing from the apex to a diameter of one and half inch, at two and half inches from 
the base; external wall very thin, it and the cast regularly marked with equal obtuse ribs, about eighty-five 
in the adult diameter of one and half inch (six in three lines), eighty at one inch (eight in three lines), 
seventy-five at nine lines and forty-six at four or five lines (ten in three lines) separated by thin equal 
equidistant slits representing lamellee, each alternate one of which is merely marginal, the others occasionally 
and irregularly uniting before reaching the centre, round which they are twisted to form a spirally conical 
central area; no connecting vesicular plates. 
The regularity and equality of size of the lamellar ribs, both on the exterior and on the cast, as 
well as their large number, gives a peculiar aspect to this species. In parts of some specimens the 
lamellar sulci are bent in a zigzag manner, but it is an unusual appearance, for which I cannot account. 
By carefully removing part of the outer wall each of the lamelle is seen to be split near the exterior (not 
visible on casts), and each to be perforated by tubuli as in Mr Lonsdale’s supposed genus Tryplasma ; 
these punctures leave no trace on the equal, obtuse, smooth, ridges of the casts. I have usually seen this 
coral ticketed in collections as Cyathophyllum turbinatum, to which it bears some superficial resemblance, 
but has no real specific or even generic relation. 
Position and Locality.—Very abundant in the Coniston limestone of Coniston, Lancashire; in the cal- 
eareous flags of Applethwaite Common, Westmoreland ; fine Caradoc sandstone of Mulock Quarry, Dalquorhan 
near Girvan, Ayrshire; flags of High Haume, Dalton in Furness, Lancashire; slates of Llansantfraid, 
Glyn Ceiriog, Denbighshire. 
Explanation of Figures —Plate 1. B. fig. 23. Average sized specimen from Coniston, shewing the 
equal lamellar sulci, and portion of the epitheea towards the base.—Fig. 24, Do. Shewing the form of 
terminal cup, with the lamellze uniting in pairs without vesicular connecting plates; and yertical fracture, 
shewing the conical twisting of the lamelle in the centre. 
