58 G. LINDSTROM, ON TIIK SILURIAN GASTROPODA AND I'TEUOPltDA OK GOTLAND. 



3. Tryblidium? radiatum u. 



PI. XVIII fig. 1, 2. 



Shell oval, iniicli clevatedly conical, the greatest height lying near the middle of 

 the longitudinal axis. The apex anterior, truncated, curved as to lean forwards over 

 the anterior margin of the aperture. The shell between the apex and the margin is 

 consequently much concave. The apertural border is straight and horizontal. The 

 surface is covered by fine, closely packed, radiating stri;a3 and a few concentric lines 

 of growth. The shell has been thick, as may be seen by a few fragments which are 

 left along the borders. The general shape of this shell has led me to place it in this 

 genus, with the other species of which it corresponds as to its outline. This is, however, 

 more elevated like a Helcion. 



Diameter from the apex to the hind edge 24 mill. The transverse diameter 20 

 millim. Height from the rim of the aperture 15 millim. Length of the aperture 

 23 mill. 



Only a single specimen has been found in the crj^stallino limestone of Wialmsudd 

 near Farosund. 



Fam. III. TECTURIDiE Adams. 

 Gen. PAL/EACM/EA Hall. 



1873. 23d Rep. on the State Cab. of N. York p. 242. 



Shell patelliform, a^terture oblongate, exterior surface concentrically wr'inkled, on the 

 interior surface near the top a lureath of muscular impressions, nearly coherent. 



It is only provisionally that the Gotland species, described below, can be placed 

 within this genus. It is chiefly in consequence of its outward shape, which most re- 

 sembles that of Pala^acmica. In Hall's specimens the muscular markings are unknown. 

 The Patelloid shells which are now and then found in the older palaeozoic strata belong 

 probably to several different genera. The "Patella)) antiquissima from the Lower Silu- 

 rian of Sweden is nearly related to Tryblidium through its series of six pairs of de- 

 tached muscular scars. The typical species of Metoptoma, which as De Koninck has 

 shown liave a coherent muscular band and consequently cannot, as Hall 1. c. has hin- 

 ted, be plates of a Chiton, agree with Lepetopsis in the conformation of this band. In 

 the Red Orthoceratite limestone of ()land at Wickleby Hr von Sciimalensee has found 

 a specimen resembling a Metoptoma and another form probably belonging to the same 

 generic group of which WriiTFiELr) has given figures in Geology of Wisconsin, vol. IV 

 pi" 3 f. L5, 17, 18, but which scarcely can belong to Metoptoma as he assumes. The 



