ROBERTS — UPPER SILURIAN CORALS. 
59 
division of Silurian Zoantliaria, differing widely from the cup- and 
star-corals, both in shape and character. They are all composite — no 
single tube or cup could be a millepore, either in fact or by courtesy, 
for the name implies the aggregation of a number of polyps having 
more direct connection with each other than the cup-corals. In 
shape they are both massive and branching. The first two genera, 
Heliolites and Favosites, are distinguished from each other by the ab- 
sence of those septa in the latter that form such elegant star-like 
discs as they fill up the calices of the former. 
Heliolites, i.e., sun-coral, is so named from the sun-like appearance 
of its calices. H. interstincta has these calices^closely set, and equal in 
distance from each other, the intervening space, called the coenenchy- 
ma, being filled with polygonal cells. Upon the surface of H. Mur- 
clmoni the calices are not closely set, and vary in approximation. H. 
megastoma is easily knowii from either ; large, closely set, calices cover 
its surface, and what coenenchyma their nearness permits is made up 
of square cells. All these are massive corals irregularly hemispheri- 
cal in form, and having a basal-plate strongly marked with concentric 
ridges. The branching HelioHtes are still more elegant. H. Grayii 
is rudely branched, and bears its sun-like calices on both surfaces. 
The only known specimen of this species was found in the Wenlock 
shale of Walsall, and is in the cabinet of its discoverer, Mr. Gray, of 
Hagley. H. inordinata is decidedly arborescent in form, very 
slenderly branched, and bearing cahces, whose rarity is made out by 
the extreme beauty of their form. This, however, is peculiar to 
Lower Silurian rocks, and I only introduce it here to complete my 
sketch of Heholitic corals. 
The genera Plasniojyora and Projwra differ from HeKolites, mainly 
in the appearance of their surfaces, the septal rays being prolonged 
beyond the edge of the caUce, and united to other rays which cover 
the coenenchyma. In every species of these three genera the number 
of septa contained in each calice is twelve. 
Next come the Favosites. These have no intervening coenenchyma, 
the coral being simply a bundle of tubes. The radiating septa of 
their calices are only developed in one species, and that a rare one, 
F. Hisingeri. F. Gothlandica is the typical form ; this has strongly 
walled tubes, t hich, coming up to the surface, cover it with a cali- 
