Dr. G. J. Hinde on the Oenus Hindia. 71 



skeletal parts, in close proximity, are many relics of a large 

 form of Palceachly a* penetrans J Duncan, and in sections the 

 passage of the tubes of the parasite through and along the 

 inside of the spicules can be seen." These tubes are said to 

 be crammed with large spores, and both tubes and spores are 

 carbonized. The parasite is further stated to "' have grown 

 at the expense of the organic matter of the spicules during 

 the lifetime of the organism " (^*. e. the sponge), and from 

 the knowledge of the physiology of the ^c7i/?/a-group it is not 

 probable that they could penetrate and live in silica [1. c. 

 p. 90). In the September number of the ' Annals ' (seven 

 years later) Prof. Duncan repeats his statements respecting 

 this asserted parasite, and still maintains that it " grew and 

 lived in the sponge as it did in the corals of the same age, and 

 was not introduced after fossilization " {I. c. p. 228). 



Considering now the character of this asserted parasite, 

 PalceachJya 'perforans^ Dune, which forms such an important 

 argument, in Prof. Duncan's estimation, for the original calca- 

 reous nature of the sponge Hindia^ the iirst point I wish to 

 notice is that, according to the author's own statement, it is 

 not probable that it could penetrate and live in silica. In 

 this case it is difficult to account for its presence in the long 

 canals and the interspaces in the examples of Hindia from 

 New Brunswick, in which Prof. Duncan noticed it, since these 

 spaces are filled with silica in the form of chalcedony and 

 quartz. This siliceous matrix is interpenetrated with the so- 

 called Pakeachlya, which Duncan asserts could not bore into 

 such mineral structures. Respecting the nature of the mineral 

 which fills up the canals and interspaces in the New Bruns- 

 wick specimens. Prof. Duncan has stated t : " The fossils are 

 infiltrated with clear transparent or rather dusky calcite, with 

 very few cleavage-planes, and in some places giving indica- 

 tions, under polarized light, of a more or less acicular or 

 fibrous structure, like aragonite. Rhombs of calcspar exist 

 here and there ; and the intensity of the colours elsewhere, 

 under the crossed Nicols, varies much." Again, on p. 90 : 

 " It does not appear to me to be likely that these parasitical 

 plants penetrated after the calcareous % fossilization of the 

 interstices was completed." The materials thus described 

 with such minuteness of detail, as calcite and aragonite, are 



• The name originally given by Prof. Duncan to the form here referred 

 to is Valceachhja perforans (Quart. Journ. Geol. Soc. 1870, vol. xxxii. 

 p, 210), and it is evident that he has here mistakenly used the term 

 "penetrans.^' I propose to revert to the original name. 



t ' Aniials,' 1879, vol. iv. p. 86. 



1^ The ifalicfi are my own. 



