258 



BULLETIN 77, UNITED STATES NATIONAL MUSEUM. 



maculae; the apertures are irregularly polygonal, five in 2 mm., with 

 thin walls; acanthopores small, four to eight or more surrounding a 

 zooecium, often occurring at the end of a fold of the wall extending 

 into the zooecial cavity. The arrangement of the diaphragms, struc- 

 ture of the walls and acanthopores, and other features brought out 

 in sections are shown in the accompanying figures and need not be 

 described. 



Although this is an undoubted, indeed, very typical species of the 

 genus, its zooecial structure has considerable resemblance to such 

 forms as Stigmatella septatuTn and S. foordii described on previous 



Fig. 150.— Oebipoea indenta. a, the type zoaritjm, natural size; b, tangential section, X20, 



EXHIBITING THE NPMEEOUS SMALL ACANTHOPORES INDENTING THE ZOCECIAL CAVITY; C, PORTION OF THE 

 SAME SECTION, X35, "WITH THE "WALL AND ACANTHOPORE STRUCTURE MORE CLEARLY SH0"WN; d, VER- 

 TICAL SECTION, X20. LO"WER ASAPHUS LIMESTONE, HALLUdDEN, ISLAND OF OELAND. 



pages. Both of the latter have numerous mesopores so that this 

 feature alone will separate them. Compared with other species of 

 Orlipora, 0. indenta is found to have smaller zooecia, thinner walls, 

 and more delicate acanthopores. The occurrence of the acanthopores 

 at the end of the infolded wall, giving the indented effect, is likewise 

 quite characteristic. 



Occurrence. — Rare in the lower Asaphus limestone at Halludden, 

 island of Oeland, Baltic Sea, where it is associated with Orhipora 

 acanthopTiora. 



The t3rpe-specimen and figured thin sections are in the collections 

 of the British Museum. 



