1848.] LONSDALE ON FOSSIL ZOOPHYTES. 99 



tubes, the boundary of which was defined by a distinct Une, arched 

 at the distal extremity, and straight or curved at the sides according 

 to the relative position of the adjacent cavities. The visible surface 

 was nearly flat or very slightly concave, and though not completely 

 preserved, was yet clearly composed of the original coral, being pene- 

 trated by minute pores similar to those in the side of vertically inter- 

 sected tubes : one limited area also presented between and around the 

 apertures a nearly smooth surface with very faint traces of boundary- 

 walls. The opening situated at the very distal extremity of the tube, 

 but in the same plane with the surface of the branch, varied in form 

 from circular to transversely oval, occupying the whole breadth of 

 the interior of the cavity ; and the margin was in general slightly 

 raised. In this part of the specimen, the space between the interior 

 of two adjacent visceral hollows was very narrow, with scarcely a 

 trace of the walls being divided medially ; but lower down, where 

 the interval was greater and the abrasion apparently deeper, a distinct 

 partition-line was occasionally visible, especially around the arched end 

 of the tube. A seemingly thickened exterior exhibited an irregular 

 surface with projecting apertures, and no signs of boundary-lines 

 either above the mouths or down the sides of the cavities, the occa- 

 sional lacunae being evidently partial abrasions. No satisfactory 

 proofs of a change in the openings were visible ; but in another branch 

 a small foramen appeared in the middle of mammillated casts, and 

 indicated an advanced stage, possibly a precursory one to a total fill- 

 ing up. 



The characters of the cavities within the branches was well shown 

 in nearly vertical translucent slices (fig. 26) and polished sections 

 (fig. 27). The difference between the breadth of the tubes imme- 

 diately adjacent to the exterior, and those in the middle area of the 

 branch was very great, where the intersection passed through the 

 centre (fig. 26) ; but that the latter were mere downward attenuations 

 of the former, no doubt could be entertained, as broad cavities were 

 traced into narrow. Nevertheless the dimensions of the tubes were 

 not always strictly uniform in equivalent positions ; circumstances 

 which affected the plan of growth evidently influenced the breadth 

 also. The total range of the cavities could not be clearly determined, 

 but it was manifestly considerable, exceeding many times the widest 

 portion ; not a trace however of a transverse lamina was detected. 

 The form was cylindrical where an interspace existed (figs. 27, 28) ; 

 but when the tubes were nearly or quite in contact, the outline was 

 more or less modified by mutual interference. In the notice on ex- 

 ternal structures, the surface is stated to consist of exposed portions 

 of visceral hollows with a flat or slightly concave outline, the aper- 

 ture being situated at the distal extremity. The equivalent part in 

 translucent slices (fig, 26) almost invariably consisted of a curved or 

 nearly straight, thin, opake layer, which did not range conformably 

 with the side of the tube, but crossed obliquely the broad extremity, 

 constituting a special structure for closing at a particular period the 

 ample tubular area. The apertures were not always apparent, yet, in 

 some cases, at the upper extremity of the oblique layer vvas a marked 



H 2 



