KONGL. SV. VET. AK A DIM I FAN HANDLINGAR. BAND. 34. \:<> 8. I .'> 



It' wc now compare (hese sections, vvhere the lenses are so distinctly seen, with 

 the more obscure sections of other Brontei, it is evidenl tli.it fche darfe points in them 

 are nothing but transformed and deteriorated centres of the lenses. In Br. platyactin 

 they are a little more distinct than in the other species. And it is with these tliat the 

 granulated spöts on the maculae of the hypostoma are most concordant. 



Bronteus sp. indet. 



IM. II figs. -28 — 30. 



r riiis species, of which only the hypostoma is known, found at Länsa, Gotland, is 

 likcly, to judge by that, to be nearly related to Br. polyactin. The shape of this hypo- 

 stoma is exactly the same and the maculse are placed in the same position, hut they are 

 larger, a little sunk on the blind surface and the group of the lenses is different. Its 

 superior margin forms an ingoing arch and the lenses themselves are not convex, but 

 rounded or slightly polyedric, and separated through thick interspaces. 



Bumastus Murchison. 



The only recorded hypostoma with maculae belongs to B. insignis Hall as described 

 by Saltee Monogr. p. 20S pl. 27 hg. 7. He says: »A pair of compressed tubercles oe- 

 enrs at the lower third: they are transverse-ovate, and more than their own diameter 

 apart. This is nearly in coneordance with what is seen on the species to be described 

 below. 



Althongh it can in reality be said that the species of Bumastus are the most com- 

 mon of all trilobites in the Silurium of Gotland, in so far that their head pieces and py- 

 gidia are raet with everywhere in the limestone rocks of the island, the tind of entire 

 specimens or of detached hypostomas is amongst the rarest events when collecting there 

 and amongst thousands of fragments, in several places entirely filling large portions of 

 the limestone rock, there have in the Swedish State museum been acquired only three or 

 four hypostomas, which we are now going to describe. 



At first we must point ont a certain resemblance which prevails between the hypo- 

 stomas and maeulae in Bumastus and Bronteus. Compare for instance Bum. sulcatus with 

 Br. platyactin and Br. laticauda. The general form is nearly the same in both and the 

 shape of the maculae almost identical but for the complete want of granulations on those 

 of Bumastus. To this resemblance must be added that there are, as known, forms of 

 trilobites which by some authors have been regarded as Brontei and b}- others, again, 

 ranked amongst the Iliamidse. 



Three species of Bumastus have been recorded as found in the Gotland strata, but 

 of one of these no hypostoma is known. Besides, to judge by the head shields and hypo- 

 stoma, there are a few new species. To begin with the most common 



K. Sv. Vet. Akml. Hnndl. Hand. 34. N:o 8 



