Coming to the _Annulose Animals_ of the Cretaceous period, there is little special to remark. The _Crustaceans_ belong for the most part to the highly-organised groups of the Lobsters and the Crabs (the Macrurous and Brachyurous Decapods); but there are also numerous little _Ostracodes_, especially in the fresh-water strata of the Wealden. It should further be noted that there occurs here a great development of the singular _Crustaceous_ family of the Barnacles (_Lepadidoe_), whilst the allied family of the equally singular Acorn-shells (_Balanidoe_) is feebly represented as well. [Illustration: Fig. 191.--_Galerites albogalerus_, viewed from below, from the side, and from above. White Chalk.] [Illustration: Fig. 192.--_Discoidea cylindrica_; under, side, and upper aspect. Upper Greensand.] Passing on to the _Mollusca_, the class of the Sea-mats and Sea-mosses (_Polyzoa_) is immensely developed in the Cretaceous period, nearly two hundred species being known to occur in the Chalk. Most of the Cretaceous forms belong to the family of the _Escharidoe_, the genera _Eschara_ and _Escharina_ (fig. 193) being particularly well represented. Most of the Cretaceous _Polyzoans_ are of small size, but some attain considerable dimensions, and many simulate Corals in their general form and appearance. The Lamp-shells (_Brachiopods_) have now reached a further stage of the progressive decline, which they have been undergoing ever since the close of the Palæozoic period. Though individually not rare, especially in certain minor subdivisions of the series, the number of generic types has now become distinctly diminished, the principal forms belonging to the genera _Terebratula, Terebratella_ (fig. 194), _Terebratulina, Rhynchonella_, and _Crania_ (fig. 195). In the last mentioned of these, the shell is attached to foreign bodies by the substance of one of the valves (the ventral), whilst the other or free valve is more or less limpet-shaped. All the above-mentioned genera are in existence at the present day; and one _species_--namely, _Terebratulina striata_--appears to be undistinguishable from one now living--the _Terebratulina caputserpentis_. [Illustration: Fig. 193.--A small fragment of _Escharina Oceani_, of the natural size; and a portion of the same enlarged. Upper Greensand.] [Illustration: Fig. 194.--_Terebratella Astieriana_. Gault.]