'Reviews, — The Floating Fen of the Danube Delta. 133 



1. The genus Atactocrinus, here carefully described, is regarded as 

 a Dicyclic Camerate crinoid of which only the following plates are 

 known : 5 infrabasals, 5 basals, 5 radials, 5 primibrachs, and 

 5 interradials, each of the last supporting 2 interbrachials. Its 

 peculiarity is that two adjoining interradii and a third opposite to 

 them separate the adjacent radials, whereas across the two remaining 

 interradii the radials meet; consequently three of the basals are 

 truncate above, while the other two are pointed. Thus the cup is 

 bilaterally symmetrical in its irregularity. 



Dr. Weller regards the genus as intermediate between the 

 Dimerocrinidae and the Rhodocrinidae, and says that "if the two 

 anterolaterals [basals] were pointed it could be . . . placed in the 

 Dimerocrinidae ". In that Family, however, the posterior interradial 

 supports three plates, not two as here and as frequently in the 

 Bhodocrinidae. The last-mentioned Family comprises a genus in 

 which the lower part of the cup is composed of the same number of 

 plates having the same general arrangement, namely Lyriocrinua. 

 In that genus, as Wachsruuth & Springer have pointed out, the 

 basals may be all truncate above or " quite frequently one or more of 

 them hexagonal, and angular at the top ". Why then is Dr. Weller's 

 specimen not a Lyriocrinus with two basals in the latter condition ? 

 In the portion preserved the only points of difference from Wachsmuth 

 and Springer's diagnosis are the slightly greater prominence of the 

 infrabasals, correlated with the less depression of the lower part of 

 the cup. This is consistent with its lower horizon, at the top of the 

 Ordovician, previously known species being Middle Silurian. The 

 ornament differs from that of the other American species, but is of 

 the same general nature as that seen in some examples from the 

 Wenlock Limestone (Brit. Mus., E 14697, E 15617). The assigned 

 columnals are higher and more bead-like than usual in the genus, 

 but in the Wenlock specimen (Brit. Mus. E 7095) the most distal of 

 the columnals preserved approach this shape. 



2. The Sainte Genevieve Limestone, of Middle Carboniferous age, 

 lies between the Kaskaskia and the St. Louis Limestone, with which 

 latter it was till recently confused. To help towards the distinguishing 

 of its fauna, the second paper describes a collection from a single 

 locality and bed. It makes known 26 new species of Lamellibranchs 

 and Gastropods. All species, old as well as new, are illustrated by 

 half-tone reproductions of photographs, enlarged two or four 

 diameters. The results are no more beautiful than are usual with 

 this process ; it is to be hoped they may prove more useful. 



It is not stated that the specimens described in these two papers 

 are preserved in the Walker Museum of Chicago University. 



E. A. Bathee. 



IV.— The Structure and History op Plav : the Floating Fen of 

 the Delta of the Danube. By Marietta Pallis. Journal of 

 the Linnasan Society, vol. xliii, pp. 233-90, 1916. 



PLAV is the name given to the floating reed fen which is found in 

 the Balta or marsh district in the delta of the Danube. It is 

 chiefly composed of the interlacing vertical rhizomes of the giant 



