480 GRAPTOLITES. 



group. They include Involutina (found in the Lias and lower Oolite). 

 Endoihyra (found in the Lias), and Parkeria (in the Upper Green- 

 sand). Hauerina commences in the Gault and survives to the Middle 

 Tertiary ; Orbitoides, which resembles a Nummulite, commences in the 

 Chalk and survives to the Middle Tertiary; in which the Triassic 

 Fldbellina also appears to becomes extinct. Other extinct Tertiary 

 genera are Loftusia and Fabularia, of the Lower Tertiary. Elipsodina 

 characterises the Upper Tertiary. 



Among the Foraminifera which appear with the Lower Tertiary 

 rocks are Vertebralina, Pe?ieroplis, Cheilostomella, Uvigerina, Tino- 

 porus, and Heterostegina. Some other genera appear with the Middle 

 and Upper Tertiaries. 1 



Hydrozoa. The Hydrozoa are for the most part unknown in a 

 fossil state, though several jelly-fish are beautifully preserved in the 

 lithographic slate of Solenhofen, and are to be seen in the Munich 

 Museum. There are a few other forms like the Palceocoryne, which is 

 found attached to Fenestella in the Carboniferous rocks of Scotland. 



The entire group of graptolites is fossil in the Cambrian and Silu- 

 rian strata. They have an axis, with cells arranged on one side or 

 both sides, and these axes are variously related to each other by modes 

 of growth. The simplest form is Graptolithus, or Monograptus, which 

 has a row of cells on one side of the axis. Didymograptus resembles 

 two individuals of Monograptus diverging from a common origin ; 

 Tegragraptus is the similar divergence of four ; and Dichograptus the 

 divergence of more than four graptolite-like forms from a common 

 centre. When the Graptolite grows in a spiral, with cells on one 

 side, it becomes Rastrites ; when it branches in a tree-like form, it 

 becomes Dendrograptus, with which may perhaps be connected the 

 ancient Oldhamia of the lower Cambrian, and the Dictyonema of the 

 Cambrian, Silurian, and Devonian rocks. 



Diplograptus has a row of cells on each side of a straight axis like 

 two simple graptolites back to back. Occasionally a Diprionodont 

 form divides into two Monoprionodont branches, as in Dicranograptus. 

 In another modification, four Graptolites diverge from a common axis, 

 like two specimens of Diplograptus crossing at right angles ; this type 

 is termed Phyllograptus 2 



Hydrocorallina. Louis Agassiz had referred the living Millepora 

 to the Hydrozoa. This genus forms a large part of the growth of 

 existing coral reefs, is represented in the Tertiary rocks by Axopora, 

 and in the chalk by Porosphcera. Professor Moseley, F.R.S., has 

 shown the allies of Stylaster to be hydroid ; 3 it is a Miocene fossil. 



In near association with these forms, Stromatopora of the Devonian 

 rocks is sometimes grouped ; and the Silurian Ldbechia has similar 

 affinities. 



1 T. Rupert Jones, Catalogue of Foraininifera in British Museum. See also 

 Carpenter, Jones, and Parker, " Introduction to the Study of the Foraminifera : " 

 Ray Society. 



2 See Zittel, " Handbuch der Palaeontologie." Lapworth Geol. Mag., 1873 

 and 1876. 3 Moseley, Proc. Royal Soc., 1876. 



