No. 2.] THE "colonies" of m. barrande. 195 



chopsis (^Peltocarls) primus, all of which reappear in the third 

 fauna. Ceratiocaris, however, occurs in d 5. Aptychopsis (or 

 FeJtocaris, Salter, as it more probably is) occurs in the Scotch 

 Upper Llandeilos, whereas in Bohemia it is confined to the base 

 of the Upper Silurians (e 1 and e 2) and to the colonies, A 

 similar, if not identical form, however, has recently been disco- 

 vered by Mr. Lap worth in the Scotch Silurians, high up in the 

 series, and I have found another closely similar form in the sand- 

 stone of the Coniston series (Caradoc) of the north of England. 



c. Cephalopoda. — This class of fossils, as is well known, has 

 been an object of M. Barraude's especial study, and his results 

 are, therefore, of the highest value and interest. The Cephalo- 

 poda are represented in the colonial fauna by thirty-six species, 

 of which all except species of Cyrtocera are referable to the genus 

 Orthoceras. The Cephalopods, therefore, abounded in the colo- 

 nial fauna, and this ai»;ain ao;rees with the state of thini>s in the 

 earlier portion of the third fauna. On the other hand, bands df) 

 and d 4, though much thicker than the colonies, have only yielded 

 altogether eighteen species of Cephalopoda, the paucity of these 

 fossils thus contrasting strongly with the abundance of trilobites. 

 It should also be remarked that the small representation of the 

 genus Cyrtoceras in the colonies (only two species being known) 

 contrasts very strongly with the total absence of the genus in the 

 second fauna, and its great abundance in the earlier phases of the 

 third fauna, twenty -six species occurring in e 1, and no less than 

 201 species in e 2. Lastly, of the thirty-six species of Cephalo- 

 poda in the colonies, not one is specifically identical with any form 

 known in the second fauna. On the contrary, thirty -one species 

 reappear on difi"ereut horizons in the third fauna, the remaining 

 five species being peculiar to the colonies. 



d. Pteropoda. — Only two species of Hyolithes occur in the 

 colonies, and both reappear in the first phase of the third fauna. 

 Neither occur in <i 5, though various other Pteropods occur in 

 this band. 



e. Gasteropoda. — Only ten species, belonging to eight genera, 

 have hitherto been found in the colonies (almost all in the Colony 

 d'Archiac). No species is common to the colonies and the second 

 fauna, but the genus Pleurotomaria occurs in both. All the 

 colonial species, however, reappear in the third fauna ; and their 

 rarity in the colonies agrees fully with their comparative scarcity 

 in e 1. 



