EAELY PALEOZOIC BEYOZOA OF THE BALTIC PROVINCES. 331 



Hallopora splendens is a fine example of that section of the genus 

 typified by the American form H. ampla (Ulrich) in which diaphragms 

 are exceedingly abundant in the mature zone and mesopores are 

 correspondingly rare. Indeed, the species under discussion is closely 

 related to H. ampla, differing especially in its more robust growth, 

 larger and more direct zocecia, and wider mature zone. H. ampla 

 has six to seven zooecia in 2 mm., its mature zone is usually quite 

 narrow, and the zooecia as a result are somewhat obliquely directed 

 at the surface. H. splendens has five zooecia in 2 mm., a wide, well- 

 developed mature zone, and rather thick walled, direct zooecia. 



The associated form, Hallopora tolli, new species, has equally large 

 zooecia, but here mesopores are numerous and diaphragms are almost 

 entirely wanting in the zooecial tubes. 



Occurrence. — Not uncommon in the Jewe limestone (Dl), Baron 

 Toll's estate, and at St. Mathias, Esthonia. 



Holotype.—Csit. No. 57466, U.S.N.M. 



Specimens and thin sections in the collections of the British 

 Museum. 



HALLOPORA DUMALIS (Ulrich). 



Text fig. 207. ■ 



Callopora dumalis Ulrich, Geol. and Nat. Hist. Surv. Minnesota, vol. 3, pt. 1, 

 1893, p. 282, pi. 23, figs. 1-8. 



Several examples of a small, frequently branching Hallopora from 

 the Kuckers shale possess the characters of the American species 

 H. dumalis, illustrated in figure 207. The zoarium consists of num- 



/ 



Fig. 207.— Hallopoea dttmalis. a to d, vie-w of fotjk bepeesentative feagments, life size; e, sueface 



OF THE SLENDER SPECIMEN, X9; /, SUEFACE OF ANOTHEE SPECIMEN, XIS, "WITH Z0aDCL4.L CLOSUEES PRE- 

 SEEVED; g, VERTICAL SECTION, X18; h, TANGENTIAL SECTION, X18. PHTi-LLOPORINA BED OF BLACK 

 RiVEE (DECOEAH) SHALES, St. PaUL, MINNESOTA. (AFTEE ULRICH.) 



erous small branches averaging 1.5 mm. in diameter, inosculating to 

 form a bushy mass. Fragments of a zoarium are shown in figures 

 207 a to d. The surface of these branches is smooth, with the zooecial 

 92602°— Bull. 77—11 23 



