Revieics — Calcareous Concretions in Coal Seams. 37 



in general, sunimariziug and extending his earlier work, and ending 

 with a discnssion of the classification of the Ichthyosaurian Order, 



An exact description of the Ichthyosaurians of the Triassic period 

 has long been wanted, because it seemed likely that they would 

 prove to be links between the typical members of the order and some 

 early group of marsh-dwellei's or land-dwellers. Dr. Merriam, in the 

 memoir before us, begins to produce the desired material, and shows 

 how in many respects the few known genera are really links in the 

 ancestral series. The Triasj^ic Ichthyosauria have relatively larger 

 limbs than their successors, and were probably less dependent on 

 a tail-fin for locomotion. The number of phalanges in the digits is 

 less than in Icltthyomunis proper ; the interclavicle is often triangular 

 in shape (not T-shaped), thus approaching that of Labyriuthodonts 

 and some primitive llhynchocephalians ; and the pelvis is large, with 

 much-expanded pubes and iscliia, as in many other early I'eptiles. 

 The sknll is short compared with the length of the trunk, and the 

 eye is not so large as in later forms. The teeth are often fixed in 

 sockets, and not quite similar in shape in diiferent parts of the jaw. 

 The atlas and axis are not fused together, and the end of the vertebral 

 column is not so sharply bent downwards in the tail-fin as in Ichthyo- 

 saicnis. The Triassic Ichthyosauria are therefoi'e less completely 

 adapted for an aquatic life than their successors in later Mesozoic 

 periods. 



Dr. Merriam classifies the Ichthyosauria in two families, Mixosauridae 

 and Ichthj-osauridfB. The Mixosauridaj are exclusively Triassic, so 

 far as known, and have been found in Europe, Spitzbergen, North 

 America, and perhaps New Zealand. 2[ixomurus is described from 

 Europe, while Cymbospondylm, Toretocnemws, Merriamia, Delphino- 

 sanriis, and Shastasaunis occur in California and Nevada. The detailed 

 descriptions are illustrated by numerous text-figures and eighteen 

 plates. 



IV. — Calcareous Concretions in Coal Seams. Bj' M. C. SiorEs 

 and D. M. S. Watsox. Phil. Trans., 1908. 



AN important and interesting paper " On the Present Distribution 

 and Origin of the Calcareous Concretions in Coal Seams, known as 

 ' Coal Balls' ", has been contributed by M. C. Stopes and D. M. S. 

 Watson (Phil. Trans., 1908, vol. cc, series B, pp. 167-218). While 

 recognizing that the origin of the ' coal balls ' or ' bullions ' is distinct 

 from that of the coal seams in which they occur, yet their investigation 

 tends to throw light on the origin of the latter. 



Analyses show that the coal balls are principally made up of 

 calcium and magnesium carbonates, in many cases in the proportion 

 in which these carbonates occur in dolomite, and altogether forming 

 90 per cent, or more of the mass. The amount of alumina and 

 silicates was found to be so minute (averaging less than 0-2 per cent.) 

 as to be negligible, showing that muddy or detrital matter was absent 

 and that practically pure plant masses were mineralized by the mixture 

 of carbonates. 



Other concretions known as ' roof ' or ' Goniatite nodules ' 

 fr(>quently contain isolated plants, but are always found in the roof 



