THE FAUNA OF THE ST. JOHN GEOUP. 135 



followed the latter plau, and thus have brought this genus into conflict with Ptychoparia ; 

 and now we find it entirely rejected on this side of the Atlantic in favour of the last 

 named genus. That Liostracus is a valid genus, I propose to show by the following facts. 



The species referred to it were first described by Angeliu under Calymene in his 

 " Palœontologica Scandinavica " (p. 23), in company with others afterwards referred to 

 Solenopleura. Two species were retained in Liostracus, and formed the basis of the genus ; 

 and to these, another species was subsequently added. An important character, which 

 Angelin expressly left undescribed, was the form of the head at the genal angle ; but 

 while he left this part of the description unfinished, if his figures be referred to, it will be 

 seen that his impression was that these angles were rounded, and did not run out into 

 long spines as in Ptychoparia. When we come to analyse the three species referred to this 

 genus by Angelin, it will be found necessary to exclude L. mutims, which, according to the 

 Swedish authorities, is an Ellipsocephalus, a genus previously described by Zenker. In 

 the fact that this species is properly referable to Ellipsocephalus, we find a confirma- 

 tion of the idea that Angelin may have had fair reason to think that the genal angles in 

 this genus should be represented as spineless. According to Linuarsson, there were four 

 species of Ellipsocephalus in Sweden, all of which agree quite nearly with the type of the 

 genus, E. Hoffi of Bohemia, in which, as is well known, the genal angles are rounded. 

 Two other Ellipsocephali, viz., E. Germari of Bohemia and E. circidus of Norway, are 

 provided with flat spines at the genal angles ; but E. circulus, at least, occurs at a higher 

 level in the Cambrian beds than the typical species, and it is a question whether the 

 affinities of the two species named are not rather with Anomocare than Ellipsocephalus; 

 at least in so far as the typical form of the latter genus is concerned. 



The spt>cies added by Angelin to his two types of the genus Liostracus was L. 

 costatus. Of this species, J. Gr. O. Linnarsson says (1869) that "the free cheeks, which 

 are not represented [in the figure] in the ' Palœontologia Scandinavica,' have corners ex- 

 tended into spines and are of abovit the same form as those of Olenus gibbosus, and to this 

 most nearly related." ' Dr. Linnarsson further adds that " L. costatns cannot be referred to 

 Ellipsocephalus on account of the [spiued] free cheeks and the form of the pygidium," and 

 says that he " has found the species in great nvxmbers, having the heads and pygidium 

 together, and not in association with any other trilobite except Agnoslus lœvigatus." If I 

 am right in my interpretation of the characters of the most typical of Augelin's three 

 species of Liostracus, a trilobite, with such a pygidium as L. coslatus is said to possess, can- 

 not be associated with Liostracus. 



Furthermore, in the lists of species accessible to the writer, drawn up by the Scan- 

 dinavian palaeontologists who succeeded J. Gr. O. Linnarsson, this species is not qiioted at 

 all. Thus S. A. Tiillberg (1880) omits it from the list of species occurring with Aguosti 

 at Andrarum ; - and W. C. Brogger does not name it among the species given in his table 

 of Norwegian and Swedish species of the Cambrian formation.^ So that we do not 

 know it to be recognised now as a valid species by the Scandinavian authors. We are 

 thus reduced to a single species (L. aculeatus) as the type of Angelin's genus Liostracus. 



In the description of this genus, as amended by Prof. Brogger, the genal angles are 



' Om Vestergotland's Cambriska och Siluriska Aflagringer, p. 71. 



- Om Agnostus-arterna de Kambriska Aflagringare vid Andrarum, Stockholm. 



' Die Silurischen Etagen 2 uiid 3, in Kristianiagebiet, Kristiania 1883. 



