DESCRIPTION OF CHALK CORALS. 275 
while the resemblance to M. Michelin’s minute production, only a line in dia- 
meter, justifies, it is conceived, a generic union. 
Only one specimen of Clyp. tubeformis was examined. Its height was rather 
more than 3 lines ; the breadth at the upper extremity was 2 lines; of the stem 
near the middle }ths of a line; and of the base 1 line; the exterior height of 
the funnel was | line ; the interior depth }, and breadth at the bottom 3ths of a 
line. The greatest breadth of M. Michelin’s figured specimen of Clyp. margini- 
porella was half that of the English coral. The tubular openings around the 
margin were not perfect, and consequently no strict comparison could be made 
with those of the Paris basin fossil; but, as exhibited, they were in contact or 
had solid interspaces ; while in the tertiary species, the edge of the apertures is 
more or less free. The form was round, transversely oval or polygonal accord- 
ing to space or mutual interference. The size varied also; but the differences 
were clearly due to interpolations, and inequalities of age. The full range of the 
visceral tubes was not ascertained: those connected with the apertures did not 
extend visibly downwards beyond the lower extremity of the funnel, terminating 
acutely ; and those in the stem had also an apparently limited upwards exten- 
sion; but their range was possibly continued inwards, and the actual end was 
probably in the marginal apertures. Respecting the central composition of the 
coral no information could be obtained. M. Michelin’s figure 27 6. indicates a 
shallow hollow, with a transverse layer; and as concerns the equivalent, ex- 
panded portion of Cly. tubeformis, the structure was apparently similar, or else 
consisted of thin lamin. Minute additional tubes appeared occasionally along 
the inner edge of the margin, and similar developments existed also on the outer 
edge, but that portion being abraded they were less distinct. No signs of a 
decided external thickening were visible,—a point of agreement with recent Tubu- 
lipore ; but there was a total want of the lamina, which in some species of that 
genus constitutes a disk-shaped base ; and in the Tub. Fungia of Mr. R. Q. Couch, 
which in mode of growth resembles Clyp. tubeformis, an investing plate’. 
Idmonea cretacea, Milne-Edwards. (Tab. XVIII. A. figs. 5 & 5a to 5h.) 
Fixed only at the base; fan-shaped, erect ; branches dichotomous, round or 
slightly compressed on the sides ; rows of tubular apertures short, projecting, 
' Consult Dr. Johnston’s British Zoophytes, 2nd edit. 7. penicillata p. 270. pl. 48. figs. 1, 2; also 
Mr. Couch’s Zoophytes of Cornwall, &c. 
