TIIK CAMI'.IMAN SYsTKM 



The Cystidea again are pla<e<l by systematic at the Wt'-in <-f 

 tin- Echinoderma, and appear ! lepn-Miit an early stage in the 

 evolution of the Kchinoderm r.u ,-. 



Two of the Lower Cambrian l'.rarhi<>p<.<ls (Lin<inl,lln and 

 Orln'culoidea) are low forms of that class, and the others, OboUlla 

 and Kutorgina, were not much more highly organised. No Linu-lli- 

 branehia have yet been found in the Lower Cambrian "f Kurope, 

 but some small fossils found in North America are referred to thi.- 

 class. The Gastropoda are represented by the genus llynlitht.* and 

 its allies, which are usually referred to the Pteropods, though 

 their real affinities are very doubtful. More typical Gastropods 

 appear in the Lower Cambrian of America and in the Middle 

 Cambrian of Scotland. 



Crustacea are represented by the Entomostraca and Trilobita. 

 The former are true Crustacea of low organisation; the latin 

 exhibit a curious mingling of characters, which have l.-'i 

 authors to exclude them from the Crustacea, but Professor Bewht-r 4 

 remarks that Trilobites show the clearest evidence of primitive 

 Crustacean affinities. 



In the Middle and Upper Cambrian Hydrozoa (Graptolite*), 

 Crinoid and Asteroid Echinoderms, Phyllocarid Crustacea, a few 

 Lamellibranchs and Gastropods, with some Nautiloid Cephalo- 

 poda make their appearance. The occurrence of Cephalopoda, 

 the highest of the Molluscan classes, suggests that the evolution 

 and development of marine Mollusca must have been especially 

 rapid during this early period of the earth's history, or else that 

 their ancestors existed somewhere long before Cambrian times. 



The following are the principal characteristic species of the 

 several faunas which have been recognised in the Cambrian > 



Lower Cambrian (OleneMus Fauna) 



Ostracoda. Leperditia cambrensis. 



Annelida. Serpulites fistula, Scolithus linearis. 



Trilobita. Olenellus Callavei, 0. Lapworthi, 0. intermedium, Olenel- 



loides armatus. 

 Brachiopoda. Lingulella primaeva, Orbiculoidea caerfaiensis, Kutorgina 



cingulata, Obolella Salteri, Acrotreta Sabi : 

 Hyolithes nrinceps, Orthotheca Gem, St.-i...theca rugOM, 



Coleoloides typicalis, Salterella pulchella, S. Maccullochi. 



Middle Cambrian (Paradaxidcs Fauna) 



Porifera. Protospongia fenestrata (S. and M.), P. major (8.).* 

 Cystidea. Protocystis menevensis (M.). 



" S. indicates occurrence in Solva Beds, M. in Menevijin. 



