Parr IIL. Sect. ii. § 2] JURASSIC, 789 
apparently brackish-water. The marine life of the period has been 
abundantly preserved, so far at least as regards the comparatively shallow 
and juxta-littoral waters in which the Liassic strata were accumulated.! 
Corals, though on the whole scarce (67 species are known), abound on 
some horizons (Astrocenia, Thecosmilia, Isastreea, Montlivaltia, Septastrea, 
&c.). The crinoids (15 species) were represented by thick growths of 
Eaxtracrinus and Pentacrinus. There were brittle-stars, star-fishes, and 
sea-urchins (Ophioglypha, Uraster, Luidia, Hemipedina, Cidaris, Acrosa- 
lenia)—all generically distinct from those of the Paleozoic periods. 
Among the crustacea, the more frequent known genera are Eryon, Glyphea, 

FSS 




Fic. 385.—Uprrer Lias AMMONITES. 
a, Ammonites (Stephanoceras) communis (Sby.) (gj); b, A. (Lytoceras) jurensis (Zieten) 
(3); ¢, A. (Harpoceras) serpentinus (Rein) (3); d, A. (Phylloceras) heterophyllus 
) @: : 
and Eryma. The brachiopods are chiefly Rhynchonella (19 species), 
Waldheimia (12), Spiriferina (8), and Thecidium (16).  Spiriferina is the 
last of the Spirifers, and with it are associated the last forms of Leptzna, 
of which five Liassic species are known from English localities (Fig. 369). 
Of the lamellibranchs, a few of the most characteristic genera are Pecten 
(25 species), Lima (23), Avicula (21), Mytilus (18), Cardinia (16), Leda (15), 
Cypricardia (12), Astarte (14), Gryphea, Pleuromya, Hippopodium, and 
Pholadomya. Gasteropods, though usually rare in such muddy strata as 
1 See R. Tate, Census of Lias Marine Invertebrata, Geol. Mag. viii. p. 4. 
