210 SYSTEMATIC PALEONTOLOGY 



Dall states that Y. Icevis Say of the Miocene of the Atlantic coast is 

 probably the ancestor. It has certain constant differences, but is very 

 closely allied. 



Y. limatula is reported by Dall from the Pliocene of North Carolina. 

 It has been found in the Pleistocene of Maryland and South Carolina. 

 In the Recent it is widespread along the shores of the North Atlantic, 

 being found in Norway, and south on the American coast as far as Cape 

 Hatteras. It also occurs on the west coast of North America. 



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

 bor, St. Mary's County. 



Collections.— -Maryland Geological Survey, Johns Hopkins University, 

 and U. S. National Museum. 



MOLLUSCOIDEA. 



Class BRYOZOA. 



Order CHILOSTOMATA. 



Family MEMBRANIPORID/E. 



Genus MEMBRANIPORA Blainville. 



Membranipora oblongula Ulrich and Bassler. 



Memiranipora oblongula Ulrich and Bassler, Maryland Geol. Surv., Mio- 

 cene, 1904, p. 407, pi. ex, figs. 2-5. 



Description. — " Zoarium incrusting, forming delicate expansions often 

 of considerable extent over shells of mollusca and other foreign objects ; 

 occasionally in superimposed layers. Zocecial apertures arranged in 

 longitudinal series, usually elongate, occupying the entire opesium, the 

 length often nearly or quite twice the width ; when normally developed, 

 elongate, ovate or subquadrate but contingencies of growth and develop- 

 ment cause many variations without, however, ever seriously affecting the 

 general plan of the specific characteristics; measuring longitudinally 10 

 or 11 in 5 mm., transversely the average is about 10 in 3 mi a. Wall 

 varying in thickness, usually about two-thirds the width of the opesium, 



