CORALS FROM THE CORAL RAG. 99 



to do away with the nominal distinction between Thamnasirea and Si/nustrea, and to 

 designate all the species appertaining to them under the oldest of the two generical names, 

 which is that of Thamnastrea} 



The group thus composed contains a great number of species, most of which belong to 

 the Jurassic or cretaceous formations. Thamnastrea aracJmoides differs from most of them 

 by the existence of a basal plate destitute of epitheca ; but it bears great resemblance to 

 some cretaceous corals, and more especially to T. acjaricites^ T. cistela^ T. conica,^ and 

 T. decipiens.^ It differs, however, from the first of these by the calices being smaller and 

 the septa more numerous ; in T. cistela the septa are, on the contrary, more numerous than 

 in T. arachnoides ; in T. conica the septa are thinner, besides the general form being very 

 different ; and in T. decipiens the septa are thicker and form only three cycla. Compared 

 to the jm-assic species, T. arachnoides may be distinguished by similar peculiarities ; thus 

 in T. concinna^ the calices are much smaller, and the septal systems more simple ; in 

 T. scitd' the septa are more delicate and closer set ; T. Li/elli^ T. dendroidea^ T. mammosa}^ 

 T. Waltoni}^ T. cadomensis}'^ and T. affmis^^ are of a dendroid or mammilose form ; in 

 T. Defranciana^^ and T. viettensis^'" the septa are again thinner, and in T. Terquemi^^ they 

 are, on the contrary, more robust; in T.fungiformi^^ they are more numerous and more 

 strongly denticulated. As to most of the new species mentioned by M. D'Orbigny,^^ their 

 characters have not been pointed out with sufficient minuteness to enable us to distinguish 

 them from the fossil described in this chapter. 



^ In so doing, we must, however, remark that one of the fossil corals of the Neocomian period, the 

 Astrea micrantha of Roemer appears to have a real styliform columella highly developed, as well as septa 

 with entire edges, characters which we erroneously attributed to Thamnastrea. If that be really the case, 

 this species must constitute the type of a distinct genus, to which the name of Holoccenia may be given. 

 The genus Centrastrea of M. D'Orbigny, (Note sur des Polyp. Foss., p. 9,) does not contain Astrea tni- 

 crantha, and the species referred to this division in that naturalist's ' Prodrome' do not, in reality, diifer from 

 Thamnastrea, their supposed prominent columella being adventitious. We also see no sufficient grounds 

 for adopting the genus Polyphyllastrea of M. D'Orbigny, the species for which it was established differing 

 from Thamnastrea only by having a greater number of septa than is commonly the case in those corals. 



2 Astrea agaricites, Goldfuss, Petref. Germ., t. i, pi. xxii, fig. 9. 



2 Astrea cistela, Defrance, Diet. Sc. Nat., t. xlii, p. 388. 



* Astrea conica, Defrance, Diet. Sc. Nat., vol. xlii, p. 387. 



5 Astrea decipiens, Michelin, Icon. Zoopli., pi. xc, figs. 12, 13. 



c Tab. xviii, fig, 3. "' Tab. xxiii, fig. 4. » t^^. xxi, fig. 4. 



9 Astrea dendroidea, Lamouroux, Exp. meth., pi. Ixxviii, fig. 6. 



10 Tab. xxiii, fig. 3. " Tab. xxix, fig. 4. 



12 Astrea cadomensls, Michelin, Icon., pi. xciv, fig. 4. 



13 Milne Edw. and J. Haime, Ann. Sc. Nat., 3'" ser., vol. xii, p. 198. 



'1 Tab. xxix, figs. 3, 4. i^ Tab. xxx, fig. 3. i« Tab. xxx, iig. 2. i^ Tab. xxx, fig. 4. 



•8 Tab. xxx, fig. 3. 



