324 



BULLETIN" 11, UNITED STATES NATIONAL MUSEUM. 



species of this genus the walls are gently undulated, but in this form 

 the undulations are so sharp that they are in reality angular. 



Occurrence. — Rare in rocks supposed to be of Lower Trenton age 

 on Big Island, Lake Winnipeg, Canada. Apparently common in the 

 Chasmops limestone at Nittsjo Ratvik, Dalarne, Sweden, and south 

 of Bodahamn, island of Oeland. 



Plesiotype.— Chi. No. 57415, U.S.N.M. 



Fig. 201.— Diplotrtpa westoni. a and 6, side and basal views of a zoaeium, natural size; c, tan- 

 gential SECTION, X8, THROUGH A MACULA AND ADJODUNG ZOCECIA; d, PORTION OF THE SAME SECTION, 

 X20; e, VERTICAL SECTION, X8, CUTTING A MACULA; /, SEVERAL TUBES OF THE SAME, X20, ILLUSTRATING 

 THE ANGULARLY BEADED MESOPORES, THE REPLACEMENT OF A MESOPOEE BY A ZOOECXUM, AND THE TABU- 

 LATION OF BOTH SETS OF TUBES. MIDDLE ORDOVICIAN (CHASMOPS) LIMESTONE, NiTTSJO RaTVIE, 



Dalarne, Sweden. 



British Museum, specimens from the island of Oeland and thin 

 sections of the figured specimen. 



Family HALLOPORID^, new name. 



This new name in place of Calloporidse becomes necessary through 

 the substitution of Hallopora for the preoccupied Callopora. The 

 family includes those integrate trepostomatous bryozoans in which 

 the zooecial tubes are thin-walled and attain their full size slowly, 



