86 G. LINDSTllOM, ON THE SILURIAN GASTKOl'ODA AND I'TKIlorODA OF GOTLAND. 



tliroujjfli the rows of a|)orturt's alonor the back and the sides, whieli, however, are prolonged 

 into curved, spine like tubes. It seems also tliat Salpingostoiua Feud. Roemeu, Leth. 

 Geogn., Ed. 1876, Taf. 5 tig. 12, is related through its enlarged aperture and an elon- 

 gated slit on the back of the last whorl. S. A. Miller in his Supplement to the Ca- 

 talogue of American Palaeozoic Fossils p. 3U4, says that "Tremanotus is a synonym for 

 Bucania. Tlie supjjosed openings on the cast represent the spines upon the back of 

 the anterior part of the last whorl of the shell)). Dut this cannot be the case, as the 

 smallest specimens already are provided with these apertures, which during the conti- 

 nued growth of the shcdl become hidden under the overlying whorls. There are no 

 signs that the borders of the apertui'es have been formed thi'ough spines or tubes ha- 

 ving been broken from them, they are even and smooth and resemble nothing more 

 than those seen in the recent Haliotis. The peculiar ornamentation of longitudinal, 

 coarse lines also augments the probability that both are nearly related to each other. 

 This must, however, be left as an open question as there are no connecting links, the 

 Tremanoti disappearing with the Silurian era and Haliotis at the earliest found in the 

 Miocene strata. 



This genus first appears in the Lower Silurian strata of Gland from the Chas- 

 mops limestone of which island, at Boda, the Swedish State Museum possesses fragments 

 of a Tremanotus closely related to Tr. longitudinalis, if not identical. 



In the strata of Gotland two species occur: 



1. Tr. Longitudinalis with whorls of circular section; 



2. Tr. compressus with whorls of elliptical section. 



1. Tremanotus longitudinalis n. 



PI. iJi f. :>;), 40, pi. IV f. 1—7. 



Syii.: Belleroiilion dilatutns 1867. LiNUSiitoM (nuc Sow.) Noiuiiui fossil. Gotlaiidiiu p. 23. It may be that 



tills species is identical with Soweuuy's B. dilatatus Sow. Sil. Syst. p. 

 027 pi. XII figs. 23, 24. According to M'Coys more elaborate descrip- 

 tion in Paheoz. Fossils ]>. 309 this species has spiral lines, but as in 

 neither work any mention is made of apertures on the dorsal keel, I 

 cannot refer ray specimens to the English ones. 



Shell thin, discoid, whorls four, visible on both sides, evenly rounded, cylin- 

 drical and of circular outline in transvei'se section. Aperture considerably enlarged, 

 with anterior or outer lip turned up as seen in tig. 3 pi. IV, without any slit, only 

 with a shallow indenture from which a small groove continues on the inside. Where 

 fragments are left of the inner stratum of the shell, as at the inner lip of fig. 1 pi. 

 IV it is smooth with only faint stria; and the lip is so much refiexed that it covers 

 more than two thirds of the wliorl on which it reclines. As this interior stratum 

 often has been destroyed, there is on the aperture commonly only seen the impression 

 of the outer side. The radiating striae all arround the aperture, seen in the same 

 figure 1, are impressions of the exterior surface which have been uncovered. The inner- 

 most opening in the middle of the apertural expansion is transverse or somewhat tri- 

 angularly cordate, pointed towards the outer lip and broad on the opposite side. The 



