MARYLAND GEOLOGICAL SURVEY 211 



rarely less, and often much thicker, the extremes observed being shown 

 in illustrations ;. surface of wall with delicate transverse striae, usually 

 sharply rounded or angular in the middle, but when very wide the 

 median line is depressed. Numerous thin spines project from the 

 walls into the apertures but they are usually confined to the posterior 

 half or two-thirds of the opening." Very abundant in the Miocene de- 

 posits of Maryland ; less abundant in the Talbot formation. 



Occurrence. — Talbot Formation. Wailes Bluff near Cornfield Har- 

 bor, St. Mary's County. 



Collections. — Maryland Geological Survey. 



Membranipora germana Ulrich and Bassler. 



Membranipora germana Ulrich and Bassler, Maryland Geol. Surv., Miocene, 

 1904, p. 410, pi. cxi, figs. 8-9. 



Description. — " Zoarium forming a delicate crust upon foreign bodies, 

 the largest seen being less than 1 cm. in diameter. Zocecia shallow, 

 arranged in curved radiating lines in which about 6 occur in 3 mm.; 

 measuring transversely, 11 to 12 of the rows in the same space. Opesia 

 large, more or less elongate-ovate, the length and width usually as 3 is 

 to 2, separated laterally from their neighbors by about half of their width, 

 enclosed by a ring-like thickening formed by a furrow separating ad- 

 joining zocecia. At somewhat irregular intervals, the interzocecial space 

 widens and is occupied by a rounded cell that may have lodged some 

 kind of avicularium. These cells vary greatly in size but are always 

 considerably smaller than the true zocecia. Occasionally the front margin 

 of the zocecium is more elevated than the rest of the circumference. No 

 ovicells observed." 



The specimens from the Talbot formation identified with this Miocene 

 species agree in all respects with the original types save that the zocecia 

 are a trifle more elongate. This difference appears to be of not even 

 varietal importance, so that for the present it seems best to refer these 

 specimens as above. 



