The radiolarians (fig. 10) have delicate spine-covered shells composed
of silica, and their remains are very abundant in certain recent marine
sediments. They may also be found as fossils and have been reported from
Devonian and Permian rocks in Trans-Pecos Texas, and probable
radiolarians have been reported from still younger beds.
[Illustration: Fig. 9. Typical Texas Foraminifera (all greatly
enlarged). (a) _Fusulina_ (Pennsylvanian). (b) _Robulus._ (c)
_Globigerina._ (d) _Frondicularia._ (b-d, Cretaceous).]
[Illustration: Fig. 10. Typical radiolarians (greatly enlarged). (a)
_Actinomma_ (Recent). (b) _Porodiscus_ (Eocene).]