Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/86

56 very small, and nearly central; there are four generative pores, the posterior pair being the widest apart, and the madreporiform body passing between them. The peripetalous fasciole is narrow, and incloses a cordiform space. Tuberculation small everywhere; but there are larger tubercles grouped within than without the fasciole, and they become smaller towards the sharply rounded ambitus. The actinosome is well in front, the anterior part being sunken; the phyllodes are distinct; the plastron is nearly smooth; and the tuberculation of the actinal surface, which is throughout small, becomes larger remotely from the ambitus.

Height inch, length 1 inch, breadth 1 inch.

Locality.—Section 1 mile west of the mouth of the Sherbrook river, lower part of cliff.

The small tubercles, the depressed shape, the equal size of the petals, the very thin fasciole, and the far forward mouth distinguish this species, which I have dedicated to the excellent palæontologist Prof. Laube.

The next group of Australian Echini is very characteristic of the Tertiary marine deposits of the southern provinces. Members of it have been found in the corresponding formation of New Zealand, in the later Tertiaries of Java, and in the Eocene, Miocene, and Pliocene strata of Europe.

Desor originated the genus Hemipatagus amongst the fossil Echini in 1858, to include some species of the old genus Spatangus, which had the following characters :—

"Little Urchins with large tubercles on the interambulacral areas. like true Spatangi, but with this difference, that none are found in the odd or posterior interambulacrum. The plastron is smooth, as if rubbed; the petals are long and spread out; there are four genital pores, and there are no fascioles."

This diagnosis separated the group from Spatangus, which has a subanal fasciole, and tubercles in all the interambulacral areas—and distinguished it from Eupatagus, which has its posterior interambulacrum without tubercles, and a subanal as well as a peripetalous fasciole. The distinctness of the group was evident enough, although the generic value given to it was a matter of doubt.

Gray had in 1855 described a fine recent Echinus under the new generic title of Maretia, and his diagnosis brought it into close relation to Hemipatagus, Desor. It has the generic characters and, in addition, an indistinct subanal fasciole; but the test is flattened.

In 1873 A. Agassiz noticed the close resemblance of the Hemipatagi and Maretia, and, considering the subanal fasciole of no moment, determined their identity.