Revieivs — G. Lindstrdm — A Silurian Fish in Gotland. 171 



Museum, sent during this last autumn several collections from the 

 Lau canal-beds, and lately there was amongst them a pair of shining, 

 oval objects, with a peculiar sculpture ; and so well preserved that 

 it was not difficult to recognize them as the dorsal shields of fishes 

 of a very ancient type. The strongly arched and shining shield- 

 plate consists of four parts grown together; a central, which is the 

 largest piece ; on each side of this a small elongate lateral piece, 

 together with, in front, a transverse rostral plate. This latter is 

 wanting in one of the specimens, and the more perfect example, 

 which lies with the front portion somewhat below the first, has a 

 small triangular process projecting from the rostrum. Both speci- 

 mens are imperfect at the back, so that the margins cannot be 

 distinguished. The surface of the shield is wrinkled with faintly 

 elevated, longitudinal lines, which on the front portion of the central 

 plate, where it meets the rostrum, are divided up into smaller portions 

 and small knobs. The lines on the rostrum run transversely; they 

 also become broken up so as to form smaller bundles. Thus each 

 of the five plates which form together the complete dorsal or head- 

 shield, has its surface-lines disposed independently. On the surface 

 of the same slab there lies a comb-shaped shining scale, also the 

 impression of another, somewhat larger. These have probably 

 formed part of the coverhig of the tail of the fish. 



The dimensions of the most complete specimen are: length 

 55 mm., breadth 32 mm., thickness -75 mm. ; the central plate 

 40 mm. long by 25 mm. wide; a lateral plate 7 mm. wide ; rostrum 

 10 mm. long, 16 mm. wide. One of the scales covers 8x4 mm. 



The whole structure of these shields indicates a fossil belonging 

 to the Pteraspidge and nearest to the genus Cyathaspis. From this, 

 however, it differs in the triangular prolongation of the rostrum. 

 With the genus Tolypelepis of Pander,' since more fully described 

 by Rohon,- it has a certain resemblance in the glistening wrinkled 

 surface, but judging from the descriptions it markedly diifers 

 in its general structure. It will require some further interval 

 to carry out a thorough investigation of the characters of this 

 Gotland fossil before naming it and assigning its position. 



Some small, almost microscopic, head scales were washed out 

 of clay at Hammarudd near Ostergarn by the Eussian paleonto- 

 logist Volborth,^ in 1860, and they have, moreover, been described 

 by Rohon. According to him they belong to two species of 

 Thelolepis, L. Ag., T. parvidens, Ag., and T. Volhorthi, Rohon, both 

 of which also occur in England and on the island of Oesel, but 

 at a still higher horizon than on Grotland. 



It is well known that a considerable number of Pteraspid fishes 

 have been found in the Upper Silurian of Galicia and Podolia,* but 



' Monog-raphie der foss. Fische des Silur. Systems der russ.-baltischen Gou- 

 verneraents ; Petersb., 18ofi, p. 60. 



2 Die obersilur. Fische von Oesel ; Mem. de I'Acad. Imp. de St. Petersbourg, 

 vii. 3, t. xli. No. 5, p. 76. 



^ Quart. Jouru. Geol. Soc. 1861, p. 5.52; Rohon. I.e. pp. 32 and 36. 



* V. Alth, Ueber die palffioz. Gebilde Podoliens. Abhandl. der k.-k. Geol. 

 Reichsan. Bd. vii. 



