440 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 6, 



where it is more rounded than behind, being there sharply oval. 

 Lateral plane higher than the antero-posterior. Fossa tolerably deep. 

 Furrow between the free ends of the septa very distinct. Margins 

 slightly everted, thin, and a little irregular. Costae very numerous, 

 very regular, faintly yet decidedly prominent, sharply dentate, the 

 dentations being delicate and numerous. Costal curves very elegant. 

 The keel between the first and third angles is really a costa, and all 

 the costae have a relation to it, passing off from it at acute angles, very 

 much as the veins of some leaves pass off from the midrib. One large 

 costa is usually followed by a very much smaller one. Septa numerous, 

 corresponding to the costae, hardly exsert, but the larger are more so 

 than the smaller. Laminae rounded above and within, not incised, 

 regularly granular, in series ; a little thicker at the wall, but some 

 are enlarged internally. Size of the septa very irregular ; anteriorly 

 two large septa join at the wall, and posteriorly all the septa have an 

 eccentric relation to the centre of the curve formed by the anterior 

 calicular margin; they do not pass from the wall at right angles. 

 Apparently there are many systems of four cycles each, and there 

 are 132 great and small septa. Columella situated very deep in the 

 coral, parietal and rudimentary. Endotheca and exotheca none. 



Dimensions. — Height of corallum between the first and second 

 angles -*- inch ; length of base between the first and third angles 

 -| inch ; length of calice a little more than -jj- inch ; breadth of calice 

 -j^ inch. 



No. 2. An older individual, stouter, and more marked by an 

 erosion. Calicular fossa deep. 



No. 3. A large specimen, more fully developed, but deficient in 

 its calicular margin. It is taller, but still keeps the peculiar form 

 of the species. Costae less sharply but well toothed. Mark of 

 erosion very visible. Septa larger, and the inner paliform enlarge- 

 ment very evident on many. Septa 140. Columella more deve- 

 loped. 



The specimens 4 & 5 are fragmentary. 



These corals resemble a produced Ceratotrochus, if such a varia- 

 tion in form could occur. The lateral or rather the anterior erosion 

 is seen in Thysanus corbicula from San Domingo. The absence of 

 endotheca proves that they are not young buds of such a genus as 

 Rhipidogyra, and includes them amongst the Turbinolicles. The 

 eccentric distribution of costae and septa is faintly seen in a fossil 

 from the chalk-marl of Lemburg — Turbinolia galeriformis, Kner (a 

 Ceratotrochus). The more or less transverse ends of the larger 

 septa are very peculiar, as is also the existence of a small amount 

 of epitheca. 



The Thysani have, in common, an eccentric arrangement of the 

 septa and costae, a lateral erosion, a badly developed epitheca, and a 

 parietal columella. 



4. Astrocqsnta decaphylla, Edwards & Haime, var. 



In the form of a short stunted branch. From the Tertiaries of 

 Jamaica ; Lower Cretaceous of Europe. Brit. Mus. 



