TITLES AND ABSTRACTS OF PAPERS 207 



As far as may be determined from memory, the specimens of Leper ditia 

 were found in a quartzitic rock forming an exposure about 10 square yards 

 in area along the upper part of a hilly area, somewhere north of Howe station. 

 From Howe station the main road to Topsfield starts off northward. About 

 a mile from Howe station another road branches off southeastward for half 

 a mile, and then curves northward across Nichol Brook. On the writer's 

 copy of Sears's map the statement north 20° west occurs on the northwest 

 side of the crossing of this branch road over Nichol Brook, and somewhere 

 in this neighborhood the Leperditia are believed to have been found. ♦ 



Evidently it is highly desirable that the Leperditia locality should be redis- 

 covered. An attempt made during the Christmas holiday week of 1919 failed 

 dismally, not even the quartzite being found. Under these circumstances, the 

 writer no longer being situated favorably for further search, it has been 

 deemed best to leave to others the task of rediscovering the Leperditia 

 locality, and the only specimen left from the original collection made by the 

 writer has been deposited with Prof. Percy E. Raymond, of Harvard Uni- 

 versity. 



The Leperditia locality lies about 17 miles east of north from Boston. The 

 desirability of rediscovering this locality has been increased by the discovery 

 by Mr. Arthur Keith, in 1915, of numerous specimens of Camarotoechia and 

 of a few other fossils about 10 miles northeast of the Leperditia locality, 

 immediately south of Glen Mills, at the corner where the road to Rowley 

 branches off eastward. Here the fossils occur at the base of a volcanic mud 

 flow. Their age is regarded tentatively as low in the Devonian. 



The ofreat variation in plate structure in the cystid genus Holocystites 

 and related genera was recalled to the members by the author of the next 

 paper and the reason for their variation was explained. Doctors O'Con- 

 nell and Jackson, Ulrich, and Foerste took part in the discussion follow^- 

 ing the paper. 



INTERCALATION OF THECAL PLATES IN HOLOCYSTITES IN CONNECTION WITH 

 THE CRITERIA UPON WHICH SPECIES CAN BE DISTINGUISHED 



BY A. F. FOERSTE 



(Abstract) 



The genus Holocystites was founded by Hall on his species Holocystites 

 cylindrif-us. This species is described by Hall as consisting of at least six 

 encircling rows of hexagonal plates, each row containing eight plates, the 

 plates of successive rows alternating with each other. In addition to these 

 six encircling rows, there is at least one additional row at the base, and at 

 the top of the theca there is a series of circum-oral plates. The number of 

 species in the Racine of Wisconsin and northern Illinois, which are strictly 

 congeneric with Holocystites cylindricus, includes at least Holocystites abnor- 

 mis and Holoryatites alternatus. 



Holocf/stites altfnnatns is of special interest, since it departs from the pri- 



