The irregular Echinoids are not known before the Upper Cretaceous in Australia, and are very common in the Tertiaries. They are distinguished by the anus (periproct) passing backward from the apex, as compared with the regular forms, and by the elongation of the test and the loss of the strong solid spines, which are replaced by thin, slender hair-like spines. The animal is thus better fitted to burrow through the ooze on which it feeds. =Cretaceous Irregular Echinoids.--= An interesting form, _Micraster sweeti_, is found in the Upper Cretaceous or Desert Sandstone of Maryborough in Queensland, which reminds one of typical European species of this genus. =Cainozoic Irregular Echinoids.--= Amongst the Australian Cainozoic Echinoids of the irregular type the following may be mentioned. The little subglobular test of _Fibularia gregata_, and _Echinocyamus_ (_Scutellina_) _patella_ (Fig. 80 C, D) are Janjukian in age. The large _Clypeaster, C. gippslandicus_ (Fig. 80 E), ranges from the Oligocene to Lower Pliocene in Victoria (Balcombian to Kalimnan), and vies in size, especially in the Janjukian, with some large species like those from Malta and Egypt. This genus includes some of the largest known sea-urchins. The biscuit urchin, _Arachnoides (Monostychia) australis_, is commonest in the Janjukian, but ranges from Balcombian to Kalimnan. A common urchin from the polyzoal rock of Mt. Gambier is _Echinolampas gambierensis_, which is also found in the Lower beds of Muddy Creek. A typical Janjukian fossil is _Duncaniaster australiae_, formerly thought to belong to the Cretaceous genus _Holaster_. Although found living, the genus _Linthia_ attained its maximum development both in size and abundance, in Janjukian or Miocene times, as seen in _L. gigas_ (having a length of 7-1/2 inches) and _L. mooraboolensis_. _Echinoneus dennanti_ is restricted to the Janjukian. Several species of _Eupatagus_ occur in the Cainozoic or Tertiary beds of South Australia, Victoria and New Zealand; _Lovenia forbesi_ (Fig. 81 C) is common in the Janjukian to Kalimnan, both in Victoria and South Australia. In the latter State also occur the following genera:--_Studeria_, _Cassidulus_, _Echinolampas_, _Plesiolampas_, _Linthia_, _Schizaster_ and _Brissopsis_. In New Zealand the following Cainozoic genera, amongst others of the irregular sea-urchins, may be cited:--_Hemipatagus_, _Brissopsis_, _Hemiaster_, and _Schizaster_ (Fig. 81). [Illustration: =Fig. 81--CAINOZOIC SEA-URCHINS.= A--Hemiaster planedeclivis, Gregory. Cainozoic (Janjukian). Morgan, S. Australia B--Schizaster sphenoides, T. S. Hall. Cainozoic (Barwonian). Sherbrooke River, Victoria C--Lovenia forbesi, T. Woods sp. Cainozoic (Janjukian). Murray River Cliffs, S. Australia ] A clypeastroid, _Peronella decagonalis_ has been described from the (?) Lower Pliocene of Papua. =Cainozoic Holothuroidea.--=