UNKNOWN ATLANTIC OR WEST INDIAN POKITES. 89 



77. Porites West Indies x. 12. (P. Americana ineertas sedis duodedma.) 



Syn. Porites macrocephala Duchassaing and Michelotti, M6m. but las Cor. Antilles, Suppl. (1864) 

 p. 95, pi. X. fig. 15. 



Description.— The corallum rises into a mass of stems— apparently thickening irregularly 

 as they rise— some remaining nearly cylindrical, while others swell into great inverted cones, 

 flat-topped, and with irregularly wavy and hulgiiig sides. Tliese processes are about 7-r> cm. 

 high and from 5 to 7 • 5 cm. thick. 



The calicles are very small (" perparvis "), crowded, reticulate and depressed. Tlie walls 

 and septa are thin, and there is usually no columella. 



This Porites, as representing an entirely new type of growth-form, is of importance. It is 

 neither an ordinary encrusting or massive form, nor a branching form, yet it may have been 

 derived from the same kind of early stage as the latter. In this ca.se, the rising corallum, 

 instead of forking, expanded into a great top-heavy mass, like an inverted cone. 



We have here then a form which could not possibly be classed in any of the imaginary 

 Lamarckian " species." It is interesting, because it enlarges the range of possible growth-forms. 

 It is unfortunate that its locaKty is not given ; we may note, however, that the bulk of Duchas- 

 saing's specimens were either from St. Thomas or Guadalupe. Its type seems to be lost ; I 

 did not see it in Paris, nor is it in Turin, since no photograph of it was included in the photo- 

 graphs of Duchassaing's types kindly sent by Count Peracca for this volume. 



78. Porites West Indies x. 13. (P. Americana incerta: sedis tertitulecima.) 

 (PL V. fig. 1 ; PI. XIV. fig. 4.) 



[British Museum.] 



Description. — The corallum rises into thick, flabellate, basal stems, 2 cm. thick, 2 cm. wide 

 at the start, and expanding rapidly to 5 cm., where it breaks up into a crowded series of 

 irregular digitiform processes, some very thick, some very thin, forking and reforking very 

 irregularly, but always at very small angles and moreover bending towanls the vertical, so that 

 there is but little expansion of the cluster. The forking results in unequal prongs, one often 

 very thick, the other very thin, the thinner often persisting for considerable lengths. The 

 living layer is only 2 cm. deep on a cluster 13 cm. liigh.* 



The calicles are large, open, subcircular, shallow depressions, about 1 • 8 mm. in diameter. 

 The wall is thin and sharp, and consists of a wall-thread, frequently wanting, running in an 

 open very pronounced zigzag. The septa are irregular as smooth threads, swollen frequently 

 into minute conspicuous clustei-s of echinulae. Where the joining threads are not seen, these 

 echinulate granules appear to form the septa. The caUcle symmetry largely depends upon the 



* See, however, observation below. 



K 



