W. D. Lang—Evolution of Stomatopora. 21 
Bajocian of Bayeux, or of Moutiers, Calvados, Normandy, and identified 
by Michelin as A. dichotoma, Lamouroux. 
Haime!? recognised d’Orbigny’s name, and under it figured a specimen 
from the Aalenian of Postlip, north-east of Cheltenham, Gloucestershire, 
in the Walford Collection, now in the Sedgwick Museum, Cambridge. 
Haime’s type, however, differs sightly from Michelin’s figure, having 
larger and less pyriform zocecia. But the chief point to be noticed is 
the extreme simplicity of characters in both. 
In a paper? on the Liassic forms of Stomatopora three lines of 
descent were traced upwards as far as the capricornus zone of the 
Lias. Two of these stocks were already differentiated to such an 
extent that it cannot be supposed that S. dichotomoides (d’Orbigny) is 
descended from them; for the simplicity of this species shows no signs 
of being secondary. It is probable, therefore, that this Aalenian form 
is the direct descendant of the third series, of which the last term was 
S. Gregoryt, mutation capricornensis, Lang, from which S. dichoto- 
moides (VOrbigny) differs only in the greater pyriformation of the 
zocecia. 
Form 3—-the Bajocian form—is the type of S. dichotomoides 
(d’Orbigny), so that Form 2 would be called S. dichotomoides 
(dV’Orbigny), mutation IMurchisonensis, according to the nomenclature 
advocated in the former paper, because it occurs in the zone of 
Ludwigia Murchisone. Otherwise the specific names remain unaltered. 
It is to be doubted whether Vine’s form S. intermixta differs at all 
from the type of S. dichotomoides. His type of this species and of 
S. Phillipsi cannot be found, though his collection is in the British 
Museum. But his figures of S. intermixta® and of S. Phillipsi* 
remain, and cannot be ignored. The diagram of S. Smitha is taken 
from the figure in the British Museum Catalogue.® The type is in 
the York Museum. 
The only form of which sufficient material is available for tracing 
the changes in characters during the life-history is in the mutation 
Murchisonensis, of which Haime’s type of S. dichotomoides is a good 
example. The following description defines this form :— 
Zoarium loose and spreading, branching only after Type I.° The 
angle at the first dichotomy is 180°, after which it diminishes regularly 
to about 45° at the sixth dichotomy. The number of peristomes 
between each dichotomy is generally one, sometimes two. There 
seems to be no regular sequence in the variation of this character. 
The length of the zoccia at the first dichotomy is about 23-385, 
increasing to 34 at the third dichotomy and gradually decreasing again 
1 J. Haime, ‘‘ Description des Bryozoaires fossiles de la formation Jurassique”’ : 
Mém. Soc. géol. France, ser. 11, vol. v (1854), pp. 168, 164, pl. vi, fig. 2. 
2 W. D. Lang: Grou. Mag., 1905, p. 258. 
3 G. R. Vine, ‘‘ Polyzoa from the Cornbrash of Thrapston’’: Proc. Yorks Geol. & 
Polytech. Soc., vol. xii (1893), p. 252, pl. xii, fig. 4. 
2G. R. Vine): loc. cit., p. 250, pl. xu, fis. 1. 
5 J. W. Gregory: Brit. Mus. Cat. Jur. Bry., 1896, p. 46, fig. 8, which is a repro- 
duction of Gregory’s figure in ‘‘ The Jurassic Bryozoa of the York Museum’’ (Rep. 
Yorks Phil. Soc., 1893, p. 58, fig. 1). 
6 For the terminology employed see Lang, ‘‘ Jurassic forms of the ‘ genera’ 
Stomatopora and Proboscina”’: Grou. Mac., i904, p. 319. 
