40 THE GREAT BARRIER REEF. 



tide, the tentacles and peristomial membranes were often expanded to twice the length and 

 dimensions exhibited in the figure. In the example photographically reproduced in Plate XXV., 

 the polyps exhibit a condition of almost complete retraction, the tentacles amid such circum- 

 stances losing their otherwise characteristic capitate contour. The genus Pectinia, to which the 

 coral is referred, has hitherto been associated only with a tropical American, Atlantic habitat. In 

 one important feature it differs essentially from the members of the genus hitherto described. In 

 all the Atlantic species the calicinal systems coalesce laterally, and so form one compact corallum, 

 whereas, in the Torres Strait type, these systems, while forming, in adult coralla, elongate, 

 variously-contorted series, are widely separated from one another. This structural feature is 

 very clearly shown in the corallum of the example here photographed, now in the British 

 Museum collection. In respect to its loosely convolute structural modification, this species 

 differs from all previously-known Pectinias in the same manner as the representatives of the 

 genus Mussa differ from Symphyllia ; and it may eventually be found requisite, on this 

 account, to institute a new generic, as well as specific, title for its distinction. 



The specific title associated with this form has been conferred as a slight recognition of 

 the hearty assistance and hospitality, on many occasions, extended to the author by Mr. Frank 

 Jardine, of Somerset, Cape York, while engaged in investigating the fish and marine fauna of 

 the Albany Pass. 



PLATE XXVI. 



ORGM-PIPE CORIL WITH EXPINDED POLYPS. 



The natural growth-conditions of this interesting species have been already illustrated and 

 described in association with Plate XVI II., reference being made, in the same connection, to the 

 coloured delineation of the expanded polyps contained in Chromo plate No. X. The example 

 here figured was obtained at Thursday Island, and photographed from life while expanded in an 

 extemporised aquarium. It is desirable to mention that the original photograph was taken on 

 an ordinary whole-plate negative, 8^ in. X 6^ in., and represented the corallum and polyps 

 in their precise natural size. In the accompanying photo-mezzotype reproduction, details are 

 enlarged to the slight extent of increasing the area of the surface, by an inch and a half, in 

 each direction. In other words, the polyps and the associated tubes maj' be regarded as 

 being, approximately, one-sixth part as large again as their natural size. 



PLATE XXVII. 



AUTHOR'S METHODS OF PHOTOGRAPHING SUBMERGED CORALS, ETC. 



There are many workers with the camera to whom, probably, the practical illustrations given 

 in this plate of the methods employed by the author to obtain photographs of naturally submerged 



