78 J. W. Jackson — Tlie Brachiopod Liothyrclla. 



from the socket-ridges by flat, or slightly concave, thin plates.^ As 

 stated previously, a thin mesial septum is present in some of these 

 forms. 



These two types appear to characterize two distinct groups of 

 species, the members of which possess certain common features. 

 The first group comprises broadly dorsally uniplicate oval shells 

 with a I'ounded front, as, for example, Z. uva, and var. noiorcadensis 

 and Zi. antarctica, a group which, according to Blochmann, possesses 

 basal spicules in the cirri; while the second group comprises shells 

 with a somewhat truncated front, and, in some cases, broad dorsal 

 uniplication, such as L. vitrea, L. sphenoidea, L. cuhensts, L. hartletti, 

 and L. stearnsi — a group without the basal spicules. The shells of 

 this group are, as a rule, much larger than those of the first group. 



By adopting the principle of classification by means of the 

 consti'uction of the brachidium and cardinalia I had already arrived 

 at the conclusion that two such groups existed. It is interesting, 

 therefore, to find that this is borne out with regard to spicnlation. 

 We have thus a standard which is of some service in the classification 

 of fossil forms, the question of spiculation being, of course, im- 

 practicable for fossils. It was on these grounds that I placed 

 L.fulva, which has a broad transverse indented band to its loop,^ in 

 the second, or L. vitrea, group. This has now happily been confirmed 

 by Blochmann's researches with regard to spiculation. From his 

 figures (op. cit., 1914, pi. x, figs. 1-4) this species appears to be 

 non-plicate with a tendency towards a truncated front. 



Other species of recent Liotliyrince still await further examination. 

 L. moseleyi, apparently a lenticular species, has a broad indented 

 transverse band to its loop.^ Its spiculation is, as yet, unknown, 

 but from tlie circumstance that a broad band appears to go with 

 weak spiculation, it is not unreasonable to assume that it will be 

 found to be of the L. vitrea type. The interior details of X. david- 

 soni and L. clarkeana are too scanty for diagnostic purposes. The 

 Antarctic Z. hlochmanni has a type of cardinalia and brachidium 

 quite distinct from that of L. uva or L. antarctica, it being nearer 

 that of L. sphenoidea.^ Its spiculation appears to be of a weak 

 character, and, therefore, more like that of the Z. vitrea series,' with 

 which I have placed it. 



From the above observations it has been seen that the presence or 

 absence of radial striation, or of a mesial dorsal septum, does not 

 assist materially in the separation of Terebratulids into generic 

 groups. On the other hand, the character of the brachidium and 

 especially the cardinalia, which owing to their role as supports for 

 important elements of the muscular system, and consequently 



' See Blochmami, op. cit., 1908, pi. xxxix ; also Fischer & Oehlert, op. cit., 

 1891, pi. iii (for L. vitrea and L. sphenoidea). 



" See Blochmann, op. cit., 1908, pi. xxxix, fig. 26 ; and Blochmann, op. cit., 

 1914, pi. X, figs. 5, 6. 



^ See Blochmann, Wissen. Ergeh. der Schived. S.-P. Exped., 1901-3, 

 Bd. vi, Lief, vii, pi. i, fig. 14, 1912. 



* Compare Jackson, op. cit., 1912, pi. i, fig. 6, with Blochmann, op. cit., 

 1908, pi. xxxix, fig. 23rt. 



