254 



BULLETIN 10G, UNITED STATES NATIONAL MUSEUM. 



the species is now therefore rather large, and it may become convenient perhaps to 

 make some restrictions. The avicularia are quite variable. Rhagasostoma cingens, 

 R. hexagonum, and R. circumvallatum Koschinsky, 1885, from the Lutetian of 

 Bavaria, have falciform onychocellaria. Rhagasostoma dutempleanum D'Orbigny, 

 ] 852, and R. pugeti Canu, 1907, of the Parisian Lutetian, have an avicularium with 

 double orifice. Rhagasostoma prominens, Canu, 1907. also from the Parisian Lute- 

 tian, possesses an avicularium with two to four false opesiules. Many Cretaceous 

 species of Rhagasostoma possess the delicate avicularia called reticulocellaria by 

 Canu. 



Such variations exist likewise in Aspidostoma. Aspidostoma giganteum Busk, 

 1854, and A. globifemm Canu, 1911, have only small frontal or marginal avicularia. 

 The other species have interzooecial avicularia. Aspidostoma poriferum Canu, 1904, 



on 



it- 



Bx17 



Cx30 

 A x17 



FIG. 66. Genus Rliagasostoma Koschinsky, 1SS5. 



A. Rhagasostoma hexagonum Koschinsky, 1885. Zooecia, X 17 (after Koschinsky, 1885). B. 

 ('. Rhagasostoma crassa, Beissel, 1865. B. Several zooecia and onychocellaria, X 17. o, passage 

 of the occlusor muscles of the mandible ; on, onyehoeellarium ; o\>, opesiule ; r, passage of the 

 elevator muscles of the mandible. 



C. Internal cast, X 30. (B, C after Beissel, 1865.) 



has an avicularium with lateral teeth, as has also A. incrustans Canu, 1908. There 

 is an avicularium with pivot in Aspidostoma flammulum Canu, 1908. Finally, 

 Aspidostoma onychoceUiferum Canu, 1911, has perhaps a real onychocellarium. 



Rhagasostoma is the Aspidostoma of the northern hemisphere. In Europe the 

 genus dies out in the Lutetian. Here, in America, it survives into the Vicksburgian. 

 In Australia it is found in the Miocene. 



Rhagasostoma dutempleanum D'Orbigny, 1852, and R. spiniferum Canu, 1913, 

 appear to form a distinct genus on account of the nature of their ovicells. 



RHAGASOSTOMA LEVIGATUM, new species. 

 Plate 39, figs. 6, 7. 



Description. The zoarium incrusts shells. The zooecia are distinct, elongated, 

 separated by a furrow ; the mural rim is complete, salient, a little broader at the 



