134 



PROCEEDINGS OP THE GEOLOGICAL SOCIETY. 



Llandovery rocks obliges me to show their specific affinity, for the 

 purpose of ascertaining the palseontological value of the Lower Llan- 

 dovery (the Upper Bala of Sedgwick). Analysis shows that, of the 

 613 Caradoc species, 103 pass to the Lower Llandovery ; but, strange 

 as it may appear, 107 are common to the Caradoc and Upper Llan- 

 dovery, although we know of the stratigraphical break that occurs 

 between the two formations. This relation is chiefly through the 

 Actinozoa, Hydrozoa, and Brachiopoda, as we might expect from their 

 bathymetrical position and habitat. 



Of the 40 known corals, 22 (or more than one half) range to the 

 Llandovery rocks, 20 occurring in the Lower and 17 in the Upper 

 Llandovery ; or all but 3 are both Lower and Upper Llandovery ; 

 and 37 species of Brachiopoda, out of the 109 known, pass to the 

 Llandovery, 33 of which are Lower Llandovery. 



Of the 16 species of Annelida, only 2 pass to the Lower and 

 Upper Llandovery, Tentaculites anglims and Cornulites serpularius ; 

 they range also to the Ludlow. 



The class Echinodermata, represented by 32 species, is remark- 

 able for the occurrence of 8 genera of Cystidea and no less than 

 23 species. They essentially characterize the Caradoc and Bala 

 rocks ; with the exception of one species (EcMnosphcerites araclx- 

 noidea, Forbes), which passes up into the Lower Llandovery, all 

 are peculiar. It is only in the Caradoc and Wenlock strata that the 

 Cystidea are a well-developed and characteristic group of the Echi- 

 nodermata ; they are replaced in the Carboniferous rocks by the 

 Blastoidea (Pentremites and Codonaster) and do not appear again. 



The Crustacea are the largest and most important class in the 

 Caradoc. The species number 146, representing 37 genera — Ireland 

 yielding 90 (the largest number of species), Scotland 78, North 

 Wales 50, and South Wales 30 ; or taking North and South Wales 

 as one area, it has 59 species, 16 genera and 21 species being 

 common to North and South Wales. Shropshire and Westmoreland 

 are nearly equal, the former having a known crustacean fauna of 

 31 species and the latter 35. The genera most largely represented 

 are Calymene 8 species, Pliacops 14, IUarnus 13, Eemopleurides 8, 

 Lichas 6, Staarocephalus 4, Acidaspis 8, Ampyx 6, Asaphus 6, 

 Cheirurus 6, and Trinucleus 5. The remaining 26 genera (many 

 of which are Phyllopods) are represented by one or few species. 

 The 37 genera of Crustacea appear or occur 217 times in the 

 geographical areas named in the table of distribution and the 

 horizons they pass to above, and the species appear 433 times. 

 This Table clearly shows us how much has yet to be done before 

 we can obtain reliable zoological data, or be assured that the 

 several classes and genera have been even yet fairly illustrated, 

 feeling at the same time that, except by exhaustive and careful col- 

 lecting, we never shall arrive at even a fair illustration of the fauna 

 of any given group. For example, the 9 genera of Caradoc Pro- 

 tozoa are represented by only 10 species, or a fraction more than 1 

 species for each genus. 8 of these genera belong to the Spongida ; 

 and only among these do any 4 of the genera, illustrated by 1 



