Febeaeuy 12, 1897.] 



SCIENCE. 



255 



3. The eyes are absent ; when they first 

 appear they are near the lateral margin, 

 and in several genera are elongated. 



4. There are no movable cheeks; when 

 these first appear they are narrow and mar- 

 ginal. 



5. There is no thorax ; this region begins 

 with one segment, and in some genera never 

 exceeds the number of 2 or 4. The pleurae 

 at first are short. 



6. The pygidium at first is quite short 

 and of one segment. 



Three local faunas, all older than Para- 

 doxides, have been made known since Ber- 

 geron wrote his paper referred to above. 

 They all show more or less the increasing 

 prevalence of larval features in the trilo- 

 bites as we go back in time. J. C. Moberg 

 has described a number of species from 

 Sweden (including two species of Olenellus) 

 in which some of the above larval charac- 

 ters are shown. 



J. F. Pompeckz has just described a pre- 

 Paradoxides fauna from Bohemia, in which 

 are a few trilobites that carry larval char- 

 acters. Thus his Ptychoparia is referred to 

 the subgenus Conocephalites, probably be- 

 cause it has a long eye-lobe. It is a primi- 

 tive form with short pleurae, if we may 

 judge from the short posterior extension of 

 the dorsal suture. His Solenopleura also 

 differs from that genus in its long eye-lobe 

 and long glabella, but these also are larval 

 features.* Another species of Solenopleura, 

 however, cited by Pompeckz has shorter 

 eye-lobes. 



It is the Protolenus fauna of the St. John's 

 group (Cambrian), however, which shows 

 most decidedly larval traits in its adult 

 trilobites. 



Among these trilobites all (so far as their 

 remains show it) have prolonged eye-lobes, 

 a peculiarity which marks the early Olen- 



*In the larval forms of Ptychoparia and Soleno- 

 pleura of the Paradoxides beds, however, the eye-lobe 

 is short. 



idcB. Many of them have longitudinal gla- 

 bellse, also a larval character. Many have a 

 short posterior extension of the dorsal su- 

 ture, indicating the primitive feature of 

 short pleurae. Many have small and weak 

 pygidia; this is inferred from the rarity of 

 this part of the organism in the collections 

 preserved. 



Protolenus (typical), which has a general 

 resemblance to Paradoxides, differs from it 

 in the absence of a clavate glabella, and 

 the small anterior lobe of this part of the 

 head-shield, but these are characters found 

 in the larval stages of Paradoxides. 



A genus of this fauna, almost as common 

 as Protolenus, is Ellipsocephalus ; this genus 

 also abounds with Protaspian peculiarities. 



Lastly, we may refer to the genus Mio- 

 macca, which has the following larval fea- 

 tures, longitudinal glabella, long eye-lobe 

 and short posterior extension of the dorsal 

 suture. If Zacanthoides of the Middle Cam- 

 brian were shorn of the long posterior ex- 

 tension of this suture and its long pleurae 

 it would not differ greatly from Micmacca. 



In the Olenellus fauna also are genera, 

 such as Olenellus, Protypus, Avalonia and 

 Olenelloides, which retain marked larval 

 characters. 



Brachiopoda. — If we turn our attention to 

 the Brachiopoda we note that they show a 

 special development in the early Cambrian 

 different from that of the Paradoxides beds 

 and the later members of the Cambrian 

 System. 



The most notable feature is the large 

 percentage of Obolidce (including Siphono- 

 treta). The older Cambrian holds, in com- 

 mon with the Paradoxides beds, the small 

 shells of Acrothele, Acrotreta and Linnars- 

 sonia; but it also has a series of larger 

 forms peculiar to it. Such are Oholus Bots- 

 fordia, Trematobolus and Siphonotreta of the 

 Protolenus fauna, and Schizamhon and Mic- 

 witzia of the Olenellus fauna. This great 

 development of oboloid shells is not re- 



