XXll DESCRIPTIVE REMARKS. 
phalopoda, is represented in this Formation by Orthoceras, fig. 16 ; these 
straight shells, divided by ‘‘septe,” and externally striated, are the 
most abundant and widely distributed of the Mollusca in Paleozoic 
strata, and attained a larger size than any other fossil shell. 
Next in Paleontological importance to the Trilobites, are the re- 
markable bodies called Graptolites, their name being derived from two 
Greek words, signifying written stone, or writing on stone. Various 
kinds of these Fossils are represented on Plateix. This group of anoma- 
lous marine animals, so abundant in these ancient strata, wherever the 
condition of the sediment (such as a fine muddy deposit, converted into 
argillaceous shale) was favourable to their existence, has, like the Tri- 
lobites, entirely passed away; their representatives at the present day 
being most probably the compound Asteroid Zoophytes, such as Virgu- 
laria, in which the polypidoms are arranged on either side of a rod; and 
other elongated forms of the Pennatulide, or sea pens, and the Sertula- 
rian Zoophytes or Corallines, belonging to the Hydrozoa, so abundant on 
our sea shores. To illustrate these, and forcomparison, see woodcut, fig. 4. 
Fig.4.— Graptolites, and probable allied recent Hydrozoa, and other Zoophytes. 
b 
WEE 
(e000 
a. b. Virgularia mirabilis; (recent), a. nat. size; b. enlarged. Die Graptolithen, &c., pl. 22, a, b, by 
Prof. Geinitz. 
cd. peruls ert (recent) ’c. nat.'size; d. enlarged portion. British Zoophytes (Johnston), pl. 
xi, figs. 5, 6. 
e. f. Diplograpsus pristis; (fossil), e. nat. size; enlaged:portion. Die Grap. pl. i., fig. 23. 
g. h. Plumularia pennatula ; (recent), g. nat. size ;.fenlarged portion. Brit. Zooph., pl. xxii. figs. 1, 2. 
t. k. Graptolithus sagittarius ; (fossil), ¢. nat. size; 4. enlarged portion. Journ. Geol. Soc., vol. viii, 
pl. xxi., fig. 8, c, d. i 
2. Graptolithus priodon ; (fossil), restored, after Forbes. 
