74 O. LINDSTKOM, ON 'I'llK SILURIAN GASTROIMlDA ANIJ I'TEHOPoOA OF GOTLAND. 



of a species with considerably enlarged aperture and narrow whorls, representing the 

 division of Bellerophons named Phragmostoina, which are of such frequent occurrence 

 in the Upper Silurian shale beds of Scania. But they are too obscure for identification. 



Conspectus of the Species: 

 I. Shell only with transverse stria;, radiating in pinnate arrangement from the 

 slit band: 



1 B. sphajra n. 



2 B. fasciatus n. 



3 B. globulus n. 



4 B. tajnia n. 



5 B. fastigiatus n. 



6 B. tubulosus n. 



II. Shell with longitudinal stri* or furrows intersecting the transverse ones ( = 

 Bucania Waagen and De Koninck). 



7 B. squamosus n. 



8 B. Eiseni n. 



9 B. elegantulus n. 



10 B. latevittatus n. 



11 B. gemma n. 



12 B. pilula n. 



III. Shell divided tlirougli two longitudinal grooves. 



13 B. trilobatus Sow. 



1. Bellerophon splisera n. 



PI. Ill tigs. 35—38, pi. V ligs. 1—16, pi. VII fig. 9. 



Shell globular, extremely thin. Surface ornamented by closely set, transverse striae, 

 which abut upon the slit band in an acute angle of 45° and curve gently outward 

 in a bow, the convexity of which is directed towards the aperture. There is some 

 variation, as shown in the figures, with larger, smooth intervals between the sti'ia;. 

 Some faint longitudinal stria; crossing them are visible in several specimens. In well 

 preserved shells and through sections in the umbilicus it is evident that many of the 

 transverse stria; have continued as free, outwardly bent, thin laminje. They have been 

 especially crowded in the uinjjilicus, where they also are most completely preserved^ 

 imbedded in the soft shale. Several figures are given on plate V, showing details in 

 natural size and magnified. Their length amounts to two millimeters and sometimes 

 more. Where they have been well protected they stand out in relief as narrow hooks. 

 These lamella; have probably, each in its turn, been the apertural border of the widely 

 expanded mouth. 



The whorls are five and a half, much rounded, and, as seen in transverse sec- 

 tions, from two to three times as broad as higli. The last whorl is much expanded near 

 the aperture, with the slit band elevated as a blunt keel. The aperture is large, trans- 

 versally oliovate, the lips rather thick, the inner lip bent down as to hide the whorl 



