60 



BULLETIN 77, TJlSriTED STATES NATIONAL MUSEUM. 



Species of Stomatopora have also been classed with the coral genus 

 Aulojiora, which has a somewhat similar growth and cell aperture. 

 This coral, however, in addition to other differences, is invariably of 

 much larger size and lacks the porous walls of the bryozoan. 



STOMATOPORA ARACHNOIDEA (Hall). 

 Text fig. 7. 



Aulopora arachnoidea'B.KLL, Nat. Hist. New York, Pal., vol. 1, 1847, p. 76, text fig., 

 pi. 26, figs. 6a-c.— Nicholson, Pal. Ohio, vol. 2, 1875, p. 216, pi. 23, figs. 1, 16. 



Stomatopora arachnoidea Nicklbs and Bassler, Bull. 173, U. S. Geol. Surv., 1900, 

 p. 419. — CuMiNGS, 32nd. Ann. Rep. Dep. Geol. Nat. Res. Indiana, 1907, p. 

 885, pi. 32, figs. 2-2c. 



The American specimens referred to this species occur in all the 

 divisions of the Middle and Upper Ordovician, and in the Richmond 

 group of earHest Silurian age. The various Russian examples having 

 ^ the characters of typical 



StomatoiJora agree in all 

 respects with S. arach- 

 noidea, save that they 

 are of slightly more 

 delicate grow^th. This 

 difference is not even 

 of varietal importance, 

 since, as shown from 

 the stud}^ of American 

 examples, a large num- 

 ber of specimens would 



Fig. 7.— Stomatopora aeachnoidea. a, portion of a delicate undou btediy remo Ve it. 



ZOARITJM, X9, GEO-WTNG UPON THE CELLULIFEEOUS SIDE OF A ThC ZOarlum ITX 



SPECIES OF HELIOLITES; 6, PART OF THE SAME, X20, ELLUS- . 



TRATING THE DETAILED STRUCTURE. LyCKHOLM LIMESTONE OtOTRatOJ)OraaraClinO'l(L6a 



(Fi), HoHENHOLM, ISLAND OF DAGO. jg ^f slcudcr, dclicate 



incrusting, frequently dividing, more or less parallel edged branches 

 made up of simple zooecia arranged in a single series. The apertures 

 are circular, somewhat exsert, and are almost as wide as the branches, 

 4 to 5 in 2 mm. ; walls of zooecia finely porous. 



There is no chance to confuse this species with any associated 

 bryozoan, save, possibly, the various forms of Corynotrypa. The 

 latter agree in their simple, unilinear, adnate growth, but differ 

 decidedly in their club-shaped zooecia. 



Occurrence. — In America this species is found throughout the 

 Middle and Upper Ordovician and earliest Silurian at various local- 

 ities in the United States and Canada. The occurrences in Russia 

 are (1) in the Echinospherites limestone (Cl), 4 miles east of Reval, 

 where a specimen was found incrusting a ramose bryozoan (Cat. No. 

 57182, U.S.N.M.); (2) a small example incrusting a crinoid plate in 

 the Kuckers shale (C2), Baron Toll's estate, near Jewe (Cat. No. 57181, 



