86 MADEEPORAEIA. 



SYSTEMATIC AEEANGEMENT OF THE SPECIES. 



Group I.— ASTRj;OPOR-ffi EXPLANATJ; 



In which the corallum spreads laterally, either encrusting or with a free edge supported hy an 

 epitheca. Tlie corallum thickens slowly and often irregularly. 



Species 1. Astraeopora expansa. (PI. XXV. ; PI. XXXIII. fig. 7.) 

 Astrceopora expansa, Briiggemann, Ann. and Mag. Nat. Hist., xix. (1877) p. 416. 



Description. — CoraUum thin and slightly crateriform, the edge rising freely, supported 

 by a well-developed concentrically wrinkled epitheca. As the central region dies, it is 

 grown over by a layer of coraUum under which a secondary epitheca appears. The outer 

 margin is about • 5 cm. thick. 



Calicles small (1 • 5-2 mm.), round, do not project above the ccEnenchyma. When the 

 corallum is held up to the Ught they appear to reach right down to the epitheca. Very 

 irregularly distributed in what appear to have been irregular concentric rows (i. e. as they 

 appeared along the growing edge). These rows may be as much as 1 cm. apart, while along 

 the rows the calicles may be as near as 2 mm. to one another. 



The cceneuchyma is composed of nearly continuous horizontal floors supported by fine 

 vertical pUlars. The wide interstices between the calicles show either such a smooth floor, 

 or else a floor showing the formation of piUars in all stages of development from simple points 

 to a flat reticuliim joining their upper ends and commencing to form a new floor. 



The unique specimen on which this species is founded exhibits the extreme explanate 

 method of growth of the genus. It has apparently developed at the edge of a previous growth 

 of the same, continuing the edge outwards on the one hand, and on the other creeping back- 

 wards over the dead growth. The specimen cannot rightly be called stalked (cf. Briiggemann), 

 the " short pedicle " being in reality a broken fragment of the previous growth, showing in 

 section the rectangular floor-and-pUlar texture of the coenenchyma. Seen from above, the 

 specimen is kidney-shaped, or even better, ear-shaped. 



This form seems to be a simple enlargement by lateral expansion of the youngest known 

 stage of Astrceopora and of its saucer-Uke epitheca. The edge of the coraUum, supported by 

 the epitheca, rises free from the substratum. 



a. Locality not recorded. [Eegister No. 58. 12. 17. 6.] (Type.) 



