MAin'T-AM) CKOI.OOICAL SURVEY 211 



TlicM' lire i(\i;;ir(|c(l ;is the Iriic zoocciii, ilic other tiil)cs Ijcin;,'' jiroljably 

 nil (if llic nature of ]ui'Soi)ores. In longitudinal sections the tubes have 

 tliiii walls, yicrforniod as usual, arc developed in any part of the axial 

 i-cgidii and a|i|irnacli the surface in a very gradual curve. No dia- 

 phragms were observed. 



No Ilelerupora has been seen by llic author tliat resembles this spe- 

 cies very closely. Indeed, there is a douljt regai'ding its belonging to 

 this genus, but, after comparing it with all the described genera of this 

 section of the Cyclostomata, it appears to agree better with JTelcropora 

 than with any of the other genera. 



Occurrence. — Aqtjia Fobmation. Upper IMarlboro. 



Collection. — Maryland Geological Survey. 



Order CHILOSTOMATA. 



Family MEMBRANIPORIDAE. 



Genus MEMBRANIPORA Blainville. 



Me:\[bbanipoea eimulata n. sp. 

 Plate LX, Figs. 1, 2. 



Description. — Zoarium adnate, forming a tliin, single sheet of indefi- 

 nite extent. Zooecia hexagonal in form, arranged quincuncially with 

 the longitudinal rows generally very regular. Apertnres occupying the 

 whole of the large opesium, quite regularly ovate in shape. Eim or 

 interapertural space narrower than the opesia, rounded, sometimes an- 

 gular in the middle but oftener with a depressed interzooecial suture 

 line, marked with close transverse lines or wrinkles. Taking the place 

 of an ordinary zooecium isolated cells or, more commonly, two or three 

 in longitudinal sequence, occur which differ from the rest in having a 

 convex cover with a narrow median slit and above the slit a linear cres- 

 centic impression. These cells may represent an unusual type of ooecia 

 but more jDrobably are to be considered as a form of vicarious avicularia 

 or vibracula. 



The specimens upon Avhich the species is founded are divisible into 

 two varieties, one with smaller zooecia and opesia and thicker walls 



