NOTES ON SILURIAN FOSSILS FROM OHIO AND OTHER 



CENTRAL STATES. 



Aug. F. Foerste. 



[Concluded from April Number.] 



In the type of Ilolocystites abnormis (Fig. 7) six horizontal 

 rows of plates are indicated distinctly. Several accessory plates 

 are intercalated between the fourth and fifth rows from the 

 top. There is a possibility of a series of very short circum-oral 

 plates. The more or less circular oral aperture apparently had 

 a diameter of five or six millimeters. At a distance of about 

 4 mm. from the oral aperture, there is an anal protuberance, 

 about 5 mm. in diameter, interrupting the uppermost row of 

 plates. The anal aperture lies along the left margin, but on 

 the rear surface of the specimen as figured by Hall. The 

 granules of this figure represent the internal casts of the numer- 

 ous vertical pores on the interior of the plates. The surface 

 probably was ornamented by low and rather numerous pustules. 



In the second specimen figured by Hall under Ilolocystites 

 abnormis (Fig. 8) accessory plates are present between the fifth 

 and sixth, and between the sixth and seventh rows from the 

 top. The protuberance along the upper left-hand margin of 

 the figure is due, at least in part, to imperfection of preservation. 



In the type of Holocystites alternatits (Loc. cit. V\\ 12, Fig. 9; 

 PI. 12a, Fig. G; see also PI. 4, Fig. 4, in the present paper) there 

 appears to have been a more or less circular aperture about six 

 mm. in diameter. About 6 mm. from this aperature is the anal 

 protuberance, about o.b mm. in diameter. From this pro- 

 tuberance the gut appears to have extended downward, ver- 

 tically, close to the inner wall of the theca for at least 5 mm. 

 The cast outlining the gut is most distinctly defined on the right 

 side. It appears possible to distinguish certain of the horizontal 

 rows of plates as primary, and others as secondary. The primary 

 plates are larger and appear to number eight in each horizontal 

 row. The secondary plates are smaller and number about 16 in 

 each row; these secondary plates alternately truncate the pri- 

 mary plates or occupy the angles between the latter. In addi- 

 tion to the primary and secondary plates there is a series of 

 accessory plates, of which a pair, instead of a single plate, trun- 

 cates the primary plates. With this interpretation in mind, the 

 anal protuberance may be said to be located between the first 

 and second rows of primary plates. These are followed, in 

 descending order, by the first row of secondary plates, the third 

 row of primary plates, another row of secondary plates, a 



233 



