Dec, 1920] Cystids and Blastoids 53 



STUDIES BY BATHER. 



In last year's numbers of the Geological magazine Bather has 

 added greatly to our knowledge of the Osgood forms of Holo- 

 cystites. In these numbers he has elaborated with his usual 

 acumen our knowledge of this genus, and has accompanied the 

 same with numerous drawings which illuminate every phase of 

 its structure. 



7. Holocystites alternatus Hall. 



(Plate IV, Figs. 1, 2, 3, 4, 5, 6.) 



Holocystites alternatus Hall, 20th Rep. New York State Cab. Nat. Hist., 1868, 

 p. 312, PI. 12, Fig. 9; PI. 12a, Fig. 6. 



Holocystites alternatus Foerste, Ohio Jour. Sci., 17, 1917, p. 233, PI. II, Fig. 4. 



In' the type of Holocystites alternatus (Plate IV, Fig. G) there are two 

 sets of plates: a primary set, conspicuously larger in size, arranged in 

 transverse rows with S plates in each row, and a distinctly smaller set 

 inserted in transverse rows between the transverse rows of primary 

 plates. Three of the rows of primary plates are lettered A, B and C; 

 a fourth row, unlettered, occurs almost at the very base of the specimen. 

 Between rows A and B, and between B and C, secondary plates were 

 inserted at all points where three sutures met, resulting in octagonal 

 outlines for the primary plates and pentagonal outlines for the secondary 

 intercalated plates, the unpaired angle of the latter being directed 

 alternately upward and downward. Between C and the lowest row of 

 primary plates there was inserted first a secondary series arranged in 

 transverse order, and above and below the latter a tertiary series was 

 added, resulting in a very elongate theca. 



A somewhat similar arrangement is noted in a specimen from the 

 same locality, Racine, Wisconsin, numbered 839, and preserved in the 

 Public Museum of Milwaukee (Plate IV, Fig. 1). The arrangement of 

 the intercalated plates immediately below some of the plates of series C 

 is very similar, but the interpretation of the lower plates requires the 

 intercalation of three transverse rows of secondary plates, all at about 

 the same time. 



Three specimens are figured from the Cedarville dolomite at Cedar- 

 ville, Ohio (Plate IV, Figs. 2, 3, 4). All of these are noteworthy for the 

 simplicity of the plate system between rows C and D, there being only a 

 single transverse series of secondary plates, with a few scattered, incon- 

 spicuous, tertiary ones. 



In a specimen from Wilmington, Ohio, the intercalation of secondary 

 and tertiary plates has been carried to an extreme, even the primary 

 plates of row B being distinctly separated. 



This Wilmington specimen is remarkable also for the excellent 

 preservation of the lines of gro\\i:h on the thecal plates. The most con- 

 spicuous evidence of growth along the margin of the larger plates is 

 formed by a flattened border, from a millimeter to a millimeter and a 

 half in width, above which the central part of each plate rises mod- 



