BRACHIOPODA—THOMSON. 7 
Terebratulina, Disculina, Megerlia, (now Miihlfeldtia), Megerlina, Kraussina, and 
Platidia, being characterised by the absence of profound metamorphoses in the develop- 
ment of the loop and by the presence of spicules, the second group which included 
Terebratula, Macandrevia, Waldheimia, Neothyris, Terebratella, &c., being characterised 
by the presence of profound metamorphoses in the development of the loop and by the 
absence of spicules. This classification has not been sustained, being replaced by that 
of Beecher (1895) in which the family and sub-family characters are drawn from 
considerations of loop development only, based on a much more extensive knowledge 
of the latter than Deslongchamps possessed. It is worthy of enquiry whether the 
presence or absence of spicules cannot be brought into line with Beecher’s classification. 
The spicules are not preserved in fossil forms, and it was quite an arbitrary as- 
sumption on Deslongchamps’ part that Terebratula possessed no spicules. All the 
recent genera of the Terebratulidae (as now restricted) of which the bodies are known 
are possessed of spicules, viz., Liothyrina, Liothyrella, Terebratulina, Chlidonophora, 
Eucalathis and Dyscolia, the only genus of which the body is unknown being Murravia, 
(Thomson, 1916, No. 1). It may therefore be assumed with some degree of assurance 
that spicules were also present in Terebratula and the other extinct genera of the family 
and that the presence of spicules is a constant character of the Terebratulidae. 
The genera of the Terebratellidae which are known to possess spicules are 
distributed at present in the sub-families as follows :— 
Dallininae : Platidia, Laqueus. 
Magellaninae : Kraussina, Megerlina, and Miihlfeldtia. 
Megathyrinae : Argyrotheca (some species only). 
I have recently (1916, No. 2) given reasons for doubting whether Kraussina, 
Megerlina and Mihlfeldtia are correctly placed within the Magellaninae, and suggested 
that they may prove to form a separate sub-family, which may also include Aldingia, 
Kingena and Laqueus. The bodies of Aldingia and Kingena are not yet known, but the 
remainder of these genera all possess spicules, and if their separation into a sub- 
family is sustained by a further study of the loop development of the higher forms, 
the presence of spicules in the Terebratellidae will then be confined to this sub-family 
alone, so far as present knowledge goes, with the exceptions only of Argyrotheca and 
Platidia. As will be seen below,* there are other grounds for doubting whether Platidia 
belongs to the Dallininae, and it is suggested that it belongs to still another sub-family. 
Besides Deslongchamps, Fischer and Oehlert (1891 and 1892) have also paid 
some attention to spicules, and have sought to use them as specific characters, but it is 
to Blochmann (1906, 1908, 1912) that we owe our fullest knowledge of their usefulness 
in this respect. He has pointed out that within the same individual the spicules vary 
in shape from point to point, and that the figuring of isolated spicules is of little value 
for specific comparison. ‘The shape and mode of arrangement of the spicules of any 
given part of the body, however, are within limits recognisably similar for different 
* Page 21. 
