FROM THE ZONE OF AMMONITES ANGULATUS. 



11 



Division. — Lithophyllace^ C^spitos.^;. 

 Genus. — Thecosmilia. 



The Thecosmilia of the Sutton Stone are principally capitate forms, that is to say, they 

 spring from a peduncle and divide suddenly. The short and fissiparous species, Thecos- 

 milia rugosa, is very common amongst the non-capitate forms, and so is the Thecosmilia 

 Michelini, Terq. et Piette. 



At Brocastle and Covvbridge the larger Thecosmilice are common, but Thecosmilia 

 Michelini forms large masses at Cowbridge, and studs blocks at Laleston. Although 

 the specimens are very numerous, still the individuals rarely attain that bush-like 

 structure which is noticed in the Continental beds. 



At Cowbridge the specimens are mostly found as casts. 



1. Thecosmilia Suttonensis, Duncan. PI. IV, figs. 7 — 9. 



The corallum has a slender and nearly straight peduncle, which gives off corallites 

 from an enlarged summit. 



The peduncle is moderately marked with transverse ridges and constrictions, and 

 does not taper symmetrically from above downwards. The epitheca is thin, and permits 

 very numerous and fine costse to be seen through it. 



The corallites springing from the parent (the peduncle) originate by intercalicinal 

 gemmation ; they are separate as regards their walls, and differ in size, being marked 

 with transverse epithecal folds and constrictions. The calices are not quite circular, and 

 their septal arrangement is irregular. The septa are unequal, and one half of them 

 extend nearly to the centre, whilst the smaller pass inwards but for a short distance. 

 The number of septa increases with the growth of the calices. In large calices there are 

 more than four cycles, and in the smaller less than three cycles, or three cycles. 



The endotheca is highly developed. 



Height of corallum l^inch. Diameter of large calice j^jths inch. Diameter of small 

 calice jgths inch. 



Locality. The Sutton Stone. In the Collection of Charles Moore, Esq., F.G.S., 

 Bath. 



This species has some resemblance to Thecosmilia serialis in its short peduncle and 

 capitate swelling ; but the retention of the circular outline by the calices is distinctive. 

 It has some resemblance in its calice to the simple calice of Thecosmilia rugosa, Laube, 

 but there is no fissiparity observed. The origin of the corallites by intercalicinal gemma- 

 tion is very distinctive, as are also the thin epitheca and the columnar shape of the 



