288 J. W. DAWSON ON THE PHOSPHATES OF CANADA. 



It has long been known that the crusts, of modern Crustaceans 

 contain a notable percentage of calcic phosphate; and Hicks and 

 Hudleston have shown that this is the case also with the Cambrian 

 Trilobites. Dr. Harrington has kindly verified this for me by 

 analyzing a specimen of highly trilobitic limestone from the Lower 

 Potsdam formation at St. Simon, in which the crusts of these 

 animals are so well preserved that they show their minutely tubu- 

 lated structure in great perfection under the microscope. He finds 

 the percentage of calcic phosphate due to these crusts to be 1*49 

 per cent, of the whole mass. It is to be observed, however, that 

 the crusts of Trilobites must have consisted very largely of chitinous 

 matter, which, in some cases, still exists in them in a carbonized 

 state. A crust of the modern Limulus, or King Crab, which I had 

 supposed might resemble in this respect that of the Trilobites, was 

 analyzed also by Dr. Harrington. It belonged to a half-grown 

 individual, measuring 5*25 inches across, and was found to contain 

 only 1-845 per cent, of ashes, and of this only 1*51 per cent, of 

 calcic phosphate. The crusts of some Trilobites may have contained 

 as large a proportion of organic matter ; but they would seem to 

 have been richer in phosphates. Next to Lingular and Trilo- 

 bites, the most abundant fossils in the formations containing the 

 phosphatic nodules are the shells of the genus Hyolithes, of which 

 several species have been described by Mr, Billings*. Dr. Har- 

 rington has ascertained that these shells also contain calcic phosphate 

 in considerable proportion. The proportion of this substance in a 

 shell not quite freed from matrix was 2*09 per cent. These shells 

 have usually been regarded as Pteropods ; but I find that the 

 Canadian primordial species show a structure very different from 

 that of this group. They are much thicker than the shells of proper 

 Pteropods ; and the outer layer of shell is perforated with round 

 pores, which in one species are arranged in vertical rows. The 

 inner layer, which is usually very thin, is imperforate. In one 

 species (I believe, the H. americanus of Billings) the perforations 

 resemble in size and appearance those in the shells of Terebratulce. 

 In another species (H. micans probably) they are very fine and close 

 together, as in some sbells of tubicolons Avorms. I am therefore 

 disposed to regard the claim of these shells to the rank of Pteropods 

 as very doubtful. They may be tubicolous worms, or even some 

 peculiar and abnormal type of Brachiopod. In connexion with 

 this last view, it may be remarked that the operculum of some of 

 the species much resembles a valve of a Brachiopod, and that the 

 conical tube is in some of them not a much greater exaggera- 

 tion of the ventral valve of one of these shells than the peculiar 

 Calceola of the Upper Silurian and Devonian, which has been 

 regarded by some palaeontologists as a true Brachiopod. I have not, 

 however, had any opportunity of comparing the intimate structure 

 of Calceola with that of these shells. Shells of Hyolithes occur in 

 the Lower Potsdam in the same beds with the phosphatic nodules ; 

 and in one of these Mr. Weston has found a series of conical shells 

 * Canadian Naturalist, Dec. 1871. 



