31 
CRETACEOUS CORALS OR ANTUOZOA 
XYII. Genus. — ISASTREA, Milne-Edwanls and Ucdme, 1851. 
Hist. Nat. cles Corall., vol. ii, p. 5;20. 
The solid corallum is very variable in shape, forming more or less convex or 
depressed masses, sessile hy a peduncle or by a large flattened base, sometimes also 
short branches arc produced ; the lower side is covered by a striated or costulatc 
epitbeca ; on the upper the calyces are irregularly distributed, of small or moderate 
size, close together, generally polygonal, being merely separated by ridges of a 
comparatively thin costo -mural mass ; the gemmation of the calyces takes place near 
their margins ; the septa arc numerous, thin, granular above, laterally provided with 
spinulose equal or very nearly equal granules ; they arc attenuated at their inner 
ends ; dissepiments are usually abundant ; the columella is generally slightly deve- 
loped, spongiose, or almost obsolete, being replaced by a twist of the inner ends of 
the septa. 
The species of Isastrea were believed only to occur in mesozoic strata, extend- 
ing through all the formations from the Trias to the uppermost cretaceous, but 
more recently some typical forms were also described from tertiary deposits by 
Prof. A. E. Ritter V. Reuss. The species apjiear to have been, however, most 
numerous and most varied during the Jurassic period, particularly the middle 
division of it ; five occur in the South Indian cretaceous beds. 
1. Isastrea expansa, StoUezka. PI. VII, Pig. 2. 
Isast. corallum plane expansiim, modice incrassatum, infra epitheea tenuiter 
striata tectum, siqjra planiusculum ; cahjeihus poly- (plerumque six-aut septem-) 
gonis, marginihus elecatis, crasse cremilatis separatis, majoribus 6 ad 8 mm. latis, satis 
concavis, septis 48 ad 60 tenuibus, ina;qualihus, dense granulatis, lateraliter sqji- 
nulatis insGuctis, septo-costis ad prbmim, secundum alque tertlum cyclum pertinen- 
tibus in margine unite calycum tubercidiforme elevatis ; columella tenuiter spongiosa. 
The peculiarity of this species consists in the costae corresponding to the three 
first cycles of septa, becoming sharply subtubercular on the elevated and rather 
sharply angular margins, which separates the calyces. This character alone 
separates it from all known Isastrea, as far as I have been able to compare them. 
The size of the calyces and the great number of septa closely correspond to 
I. morchella, (Reuss), from the Alpine Gosau deposits, but in this species the coral- 
lum is always convex, often pedicellate, and the columella in the calyces is much 
less developed. All the septa are unusually finely and densely granular above and 
also laterally. 
Locality.— Odmm, in hvovra earthy limestone ; not common. I have examined 
three fragments which unmistakably belong to the same species; the largest is 
figured. 
Formation. — Ootatoor group. 
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