270 Reviews — Professor G. Lindstrom on HelioUtidce. 



ridge, and under these circumstances it seems natural to suggest 

 that after all the Fluela, Dischma, and Sertig, as well as the 

 Schlappina, may have been original tributaries of the Landquart. 



In this case there is no longer any difficulty in understanding the 

 cutting of the mountain barrier just mentioned. The old river 

 system would have had a much more usual character and would 

 naturally take its place among similar systems in the surrounding 

 mountains.^ And lastly, if we accept this view, we are no longer at 

 a loss to explain the anomalous physiographic features of the Davos 

 valley, but, on the other hand, are in a position to offer a simple 

 solution of its problems. 



I^ S "^TI IE ^W S. 



X, EeMABKS on the HELIOLITIDiE. B}' Gr. LlNDSTROM. KoUg. 



Svenska Vetenskaps-Akad. Handlingar, Bd. xxxii, No. 1. 4to ; 

 140 pp., 12 plates. (Stockholm, 1899.) 



UNDER the above modest title Professor Lindstrom has brought 

 out a very important work dealing with the Heliolitidee, a well- 

 known family of Palaeozoic Corals. At first intended as a review 

 of the Swedish species merely, the scope of the work was afterwards 

 enlarged, so that it now comprises a critical description of nearly 

 all the known forms of this family, and it may be considered as 

 a monograph of the group. The value of this work to the palaeonto- 

 logist depends not so much on the descriptions given of new and 

 rare forms as on the very thorough and complete manner in which 

 the author has investigated the structure of known species, by means 

 of microscopic sections, and by this means establishing the detailed 

 features by which one species may be distinguished from another. 

 The characters assigned to the earlier known forms of this group 

 were very frequently limited to those shown on the surface merely, 

 and as these are in many instances very similar in species having 

 a different internal structure, much confusion has consequently 

 resulted. The author has spared no pains to ascertain the micro- 

 scopic structural characters of the types of the known species, and 

 these are represented with marvellous fidelity in the magnificent 

 series of plates accompanying the memoir, and thereby much of the 

 uncertainty respecting these species will be removed. 



The earliest horizon on which the Heliolitidee make their 

 appearance is nearly at the summit of the Lower Silurian 

 (Ordovician), none having been found below the Bala beds in 

 England or the Wesenburg beds of Estland, whilst their highest 

 limit is the lowest beds of the Upper Devonian. They have a very 

 wide geographical distribution, as they are found in most countries 



1 Thus, the direction of the Fluela, Dischma, and Sertig is . exactly the same as 

 that of the eastern tributaries of the Inn, such as the Bernina and Chamuera. Again, 

 their relationship to the present Lareterbach and the Landquart may be exactly 

 paralleled north of the Ehatikon by the conditions existing between the Valzavenz 

 and Vergalda, the Gargellenthal and the Montafun. 



