CORALS OF THE CRAG. 5 



cicatrized,, and becomes rounded, at the same time that it expands laterally, as does the 

 rest of the corallmn, which ceases to be cylindrical, and assumes a compressed form 

 (figs. \g and 1/^). Soon after the peduncle begins to become thin, and to shorten (fig. It) ; 

 the absorption continues till it disappears completely, and the under edge of the corallum 

 becomes long and obtuse. While these modifications are going on, other changes are 

 produced in the internal structure of the corallum. As soon as the tertiary septa appear, 

 the columella begins to rise, and the primary and the secondary septa, which have become 

 rather broad, give off some spiniform trabiculae, that unite with the columella. The 

 simultaneous development of the twelve tertiary costae also determines considerable change 

 in the general - form of the corallum ; the calice, instead of being horizontal, becomes 

 arched (figs. \g, \h, \i), and the sides of the wall corresponding to the long axis of the calice 

 not having yet expanded towards the basis, the corallum has the form of a small battledore ; 

 but when the tertiary costae increase in size, the convexity of the calice diminishes, and 

 the base of the corallum spreads out, till it assumes the form of a broad, obtuse wedge 

 (figs. 1, la), which it retains in the adult state. 



The Sphenotrochus intermedins is easily distinguished from Sphenotrochus crispus, 

 S. mixtus, S. pulcheUus, S. granulosus, and S. semigranosus (species which all belong to the 

 Eocene period), by the costae being smooth, and not formed by a series of large granules. It 

 resembles S. granulosus by its general form, and S. crispus by its calice. We are acquainted 

 with only three other species, which have also smooth costae, and have often been confounded 

 with S. intermedins. One of these laevicostate species is the S. Andrexoianus, which lives 

 on the coasts of Cornwall and of the Isle of Arran, but is easily distinguished by its narrow 

 subconical base, and the slight elongation of its calice, the two diameters of which are as 

 100 : 120. The second laevicostate species, which we designate by the name of Sp/ieno- 

 trocJius Bcemeri, 1 differs also from S. intermedins by its narrow base. The third species, 

 S. Milletianus, bears great resemblance to the latter, and belongs to strata occupying the 

 same geological formation, a circumstance that has also contributed to create confusion 

 between them. But the S. Milletianus found in the Ealuns of Anjou is characterised by 

 its lateral costae being much less prominent, and its base being more rounded and less 

 compressed than in the S. intermedins. 



This fossil is common in the Coralline Crag, and the Red Crag at Sutton. , We have 

 ascertained its identity with the species found in the Crag of Antwerp, by comparing it 

 with the specimens belonging to the collection of M. H. Nyst, at Louvain, and with that 

 of Goldfuss, in the Poppelsdorf Museum, at Bonn. Specimens of this species exist in the 



1 This undescribed species has most of the characters of S. mixtus, but the costae are all similar and 

 smooth. The lateral ones are not notably larger than the others, and those adjacent are slightly curved 

 near their lower end, and sometimes interrupted. The primary and secondary septa are equal, and those 

 of the third cyclum are narrow ; all are thick towards the outer edge, and but slightly granulate. Calice 

 twice as long as it is broad. Length two lines ; breadth one line and a half; thickness one line. A fossil 

 of the Miocene strata of Cassel and Hildesheim, belonging to the Museum of Bonn. M. Nyst possesses a 

 specimen of the same species found in the Crag of Antwerp. 



