CORALS FROM THE GREAT OOLITE. 115 



Isastrea limitata differs from /. heliantlmdes} I. explanata,^ I. Munsterana,^ I. crassa,^ 

 I. lameUosissima,^ I. Bernardana,^ T. tenuistriata^ I. ornata^ and I. serialise by the small 

 size of its calices, and by its septa being more numerous. It differs from /. poli/f/onalis^^ 

 I. ohlonga}^ and /. MicheUni}' by its walls being very thin, although well formed ; from 

 /. explamdata}'^ by the concavity of its calices, and from /. Richardsoni^* by the tenuity of 

 its septa. It bears strong resemblance to T. Guettardana}^ but in the latter the calices are 

 rather deeper, and the septa more delicate, less numerous, and developed in a more equal 

 manner. Having lately been enabled to examine the fossils mentioned by M. D'Orbigny 

 under the names of Protiastrea alimena and P. Luciensis}^ we have no longer any doubt 

 as to their being specifically identical with the coral here described. We are also inclined 

 to think that the two fossils for which the same author has established the genus Dendras- 

 treaP are only subdendroid varieties of Isastrea limiiata ; but they are too ill preserved for 

 us to be able to decide the question. 



3. Isastrea explanulata. Tab. XXIV, figs. 3, 3r/. 



AsTREA EXPLANULATA, M'Coy, Ann. of Nat. Hist., s. 2, vol. ii, p. 400, 1848. 



Corallum massive, terminated by an almost flat surface. Calices shallow, not very 

 unequal, polygonal. Walls rudimentary, but the corallites distinct, even when deprived of 

 a mural investment, and the costal edge of their septa alternating in general with those of 

 the adjoining corallite. Columella rudimentary. Septa thin, closely set, straight or slightly 

 bent, striated laterally, delicately and regularly denticulated along their upper edge, and 

 very unequal in size. In general three complete cycla, and a few septa belonging to a 

 fourth cyclum appearing in a very irregular manner ; sometimes one half of certain systems 

 being more developed than the other ; sometimes the septa of the fourth order are formed 

 without being accompanied by those of the fifth, which equally enter into the composition 



^ Astrea heliantho'ides, Goldfuss, Petref. Germ., pi. xxii, fig. 4a. 

 2 Tab. xxiv, figs. 3, 3a. 



■^ Prionastrea Munsteriana, Milne Edwards and J. Haime, Ann. Sc. Nat., t.xii, p. 13G. 

 * Agaricia crassa, Goldfuss, Petref. t. xii, fig. 13. 

 ^ Astrea lamellosissima, Michelin, Icon., pi. vi, fig. 1. 

 ^ Prionastrea Bernardina, D'Orbigny, Prodr., t. i, p. 293. 

 7 Tab. XXX, fig. 1. 



^ Prionastrea ornata, D'Orbigny, Prodr., t. i, p. 293. 

 9 Tab. xxiv, fig. 2. 



1^ Astrea polygonalis, Michelin, Icon., pi. iii, fig. i. 

 n Tab. xii, fig. 1. 



12 Montastrea Michelini, De Blainville, Diet. Sc. Nat., t. Ix, p. 339. 

 >3 Tab. xviii, fig. 1. i' Tab. xxix, fig. 1. 



'5 Astrea formosissima, Michelin, Icon., pi. vi, fig. 24. (Non Sowerby.) 

 i« Op. cit., vol. i, p. 322. 

 17 Dendrastrea Langrimensis, D'Orbigny, and D. dissimilis, D'Orb., Prodr., vol. i, p. 322. 



