416 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 6, 



intercalicular furrow not so distinct as in the typical form of the 

 species. Diameter from -i- to \ inch. Septa large at the margin, 

 more or less thin elsewhere ; in six systems with a very irregular 

 septal distribution. In young corallites there are two cycles, and 

 a third in two systems (eight large septa). In larger corallites 

 there are three cycles in four systems, and two in the rest (ten 

 large septa). In the largest there are three cycles in all systems but 

 one (eleven large septa). In some large corallites a fourth cycle 

 evidently existed near the calicular margin. 



In some specimens the marginal enlargement of the septa is ren- 

 dered less distinct by rather thick and not very linear septal deve- 

 lopment internally. The corallum is too large to admit of all the 

 corallites being badly developed, except those with four cycles ; and 

 the expression of its septal number must be three cycles, the third 

 being occasionally wanting in some systems, and four cycles being 

 the extreme range. The variability in the septal number is very 

 characteristic of this variety. The exothecal dissepiments are abun- 

 dant, and bifurcate here and there. 



Marl-formation of Antigua. Coll. Geol. Soc. 



d. Yar. nobilis. PI. XIII. figs. 2 a, 2 b. 



Corallum large, irregularly convex, and gibbous above. Corallites 

 distinct, circular in transverse section, varying in size ; coenenchyma 

 well developed. Septa very large at the wall, linear within, number 

 of large-headed septa remarkable ; primary, secondary, and tertiary 

 septa often equally large. Calices varying in size. Septal number 

 from three to four cycles. This form is between the varieties mag- 

 netica and jpulchella. Coll. Geol. Soc. 



e. Yar. minor. PI. XIII. fig. 6. 



Corallites tall, slender, crowded, distinct ; walls circular, not thick. 

 Calices circular, somewhat variable in size ; the largest is -^ inch in 

 diameter. The larger septa are spear-shaped, the smaller linear ; they 

 are in six systems of two cycles ; rarely three cycles in two systems in 

 some corallites. Primary septa much larger than the secondary, but 

 nearly equalling them when there is a third cycle. Columella large. 



The alternate large and small, spear-shaped and linear septa are 

 very well seen in this form. The same details as in this form are 

 found in several specimens with larger corallites. 



Marl-formation of Antigua. Coll. Geol. Soc, and Mr. W. AY. 

 Jones's Coll. 



/. Yar. Nugenti. PI. XIII. fig. 5. 



The specimen upon which this variety is founded has no calices, 

 but the transverse views of the corallites are very distinct. 



Corallites ^ inch in diameter, not crowded. Septa in six systems, 

 two cycles in four systems and three in the other two. The tertiary 

 orders are small, and often join the secondary near the columella. The 

 primary septa are square and large at the wall, and not very linear, but 

 staff-shaped within ; their width at the margin is jL- inch. The 

 secondary septa are very much smaller and thinner than the pri- 

 mary, but nearly as large when the tertiary orders are present. 



