498 FORAMTNIFERA : RECEPTACULITES J LITUOL1DA. 



380. It is not a little singular that a peculiar Fossil, to which 

 the name Recentaculites has been given, and which has been 

 supposed by some to be a Sponge and by others to be a Coral, 

 should prove to be a gigantic Orbitolites. Specimens of this fossil 

 have been found in the Silurian Limestones of Canada, of which 

 the diameter must have been 12 or 14 inches, and their thickness 

 half an inch ; yet, notwithstanding this enormous excess in size, 

 the internal casts, produced by infiltration of their chambers with 

 Siliceous minerals (§ 390), correspond so precisely in the form and 

 arrangement of their parts with the Sarcode-body of the recent 

 Orbitolites, as described in the last paragraph, that no reasonable 

 doubt can be entertained as to the essential similarity of these two 

 types.* — It is highly probable that several other problematical 

 Fossils of the earlier Geological Epochs (such as the Stromatovor a 

 of the Silurian and Devonian formations), will be shown by Micro- 

 scopic examination to have a Foraminiferal character. The deter- 

 mination by this means of the Foraminiferal structure of Eozoon 

 Canadense (§ 397), — a Fossil occurring in Rocks so much more 

 ancient, that the existence of Animal life at the period of their 

 formation was previously almost universally disbelieved-in, — may 

 be considered one of the most important contributions which 

 Microscopy has made to Geological Science. 



381. Lituolicla. — In certain forms of the preceding family, and 

 especially in the genus Miliola, we not unfrequently find the Shells 

 encrusted with particles of Sand, which are imbedded in the proper 

 shell -substance. This incrustation, however, must be looked on as 

 (so to speak) accidental ; since we find Shells that are in every 

 other respect of the same type, altogether free from it. A similar 

 accidental incrustation presents itself among certain Vitreous and 

 tubular Shells (§ 385 ) ; but here, too, there is a basis of true Shell, and 

 the Sandy incrustation is often entirely absent. There is, however, 

 a group of Foraminifera in which the true Shell is constantly and 

 entirely replaced by a Sandy envelope ; the Arenaceous particles 

 not being imbedded in a shelly cement, but being held together 

 only by an organic glue. If the saud be Siliceous, the ' test' of 

 course has that composition ; and this envelope often bears such a 

 resemblance to a true shell exuded from the animal, as to have 

 been mistaken for it by some excellent observers. + It is not a 

 little curious that the forms of these Arenaceous ' tests ' should 

 represent those of many different types among both the Porcel- 

 lanous and the Yitreous series ; whilst yet they graduate into one 

 another in such a manner as to indicate that all the members of 

 this Arenaceous group are closely related to each other, so as to 



* See Mr. Salter's Memoir on the Genus Receptaculites in the First 

 Decade of "Figures and Descriptions of Canadian Organic Remains," 

 Montreal, 1859. 



1 It is the conviction of the Author, as of his friends Messrs. Parker 

 and Rupert Jones, that there is not really any true siliceous shell 

 (analogous to that of Folycystina) in the entire group of Foraminifera. 



