154 G. LINDSTRÖM, ON THE SILURIAN GASTROPODA AND PTEROPODA OF GOTLAND. 



is open, narrow at its mouth, most widened in the midst of the shell. The columel- 

 lar tube is consequently of unequal width, being inore narrow where the callosities are 

 opposite, and widening below them and in consequence its contours form zigzag lines 

 as shown in lig. 65. H. 16 millira., br. 23 millim. 



Found in the limestone of Wialmsudd near Fårösund and at Länsa in Fårö. 



2. Pycnomplialus acutus n. 



PI. XVI fig. 1—6. 

 ? PlalyscMsma helicites Sow. Siluria 4tli Ed. pl. 34 f. 14 — 15. 



Shell, trochiform with short spira of seven whorls. The surface is covered by 

 line, densely set, equal strise, meeting in an acute angle from both the apical and the 

 umbilical sides, where the sharp, dividing keel is projecting on the median line of the 

 whorls. At regular distances there are deeper or more distinct transverse furrows, 

 dividing the small stri« in narrow fields. The umbilicus is open and much wider 

 than in the preceding species. The aperture is transversally elliptical. The outer lip 

 widened into a prominent angular apex, forraing the keel, the inner lip thickened in 

 its upper part, nearly thrice as thick as the outer lip. A very iudistinct spiral line 

 accompanies the keel on its inferior side- H. 10 millim., br. 25 niill. Several speci- 

 mens have been found in the Trimerella limestone of Wialmsudd together with P. 

 obesus. It has also been found in the shales of Westergarn and Djupvik in Eksta and 

 in the limestone of Östergarn, Ardre, Wisby (Kyrkberget) and Nyhamn in Lummelund. 



It is possible, that this species is identical with the Silurian Platyschisma helici- 

 tes Sow. Sil. Syst. But I have not been able with any certainty to make out this 

 identity, as there are such conflicting opinions in the fourth Edition of Siluria, where 

 on page 162 a figure of it is given, quite dififerent from that on plate 34 fig. 14 — 15. 

 Both can hardly represent the same species. The first figure rather resembles a va- 

 riety of Euomphalus Walmstedti, and the second, again, which, however, consists of 

 mera nuclei, seems to coincide more with P. acutus. But if this be the case, that 

 species cannot be retained in the genus Platyschisma, as it is expressely stated that this 

 genus has »a very wide, shallow sinus in the middle of tha outer lip»^). There is not 

 the least trace of any sinus in the Gotland specimans. 



3. Pycnomplialus trochiformis n. 



Pl. XVI fig. 7. 



Shell large, broadly conical, of at least seven whorls, slowly increasing in height^). 



Sides even, without any convexity, of rectilinear outline. Surface of the only specimen 



') Mac Coy Pal. Foss. p. 533. 



^) The ratio of increase in the only 



specimen 



IS: 







Whorls. 



Height. 



B 



readth. 



1 



8 





31 



2 



6 





26 



3 



5 





20 



4 



4 





14 



5 



3 





10. 



