Page:Scientific results HMS Challenger vol 18 part 1.djvu/523

Rh Dimensions.—Major axis 0.12, minor 0.08; pores 0.06 to 0.012, bars 0.003; main axes of the medullary shells 0.05 and 0.025.

Habitat.—Indian Ocean, between Socotra and Ceylon, surface, Haeckel.

8. Prunulum fenestratum, Haeckel.

Actinomma fenestratum, Stöhr, 1880, Palæontogr., vol. xxvi. p. 94, Taf. iii. fig. 2.

Cortical shell thick walled, rough, with irregular, roundish pores, once to three times as broad as the bars; twelve to fourteen on the half equator. Proportion of the two axes = 9 : 8. Both medullary shells ellipsoidal. (The pores in Stöhr's description are by mistake called "regular"; in the figure they are very irregular, as also in the fossil specimens observed by myself. Between the cortical pores arise very short irregular thorns.)

Dimensions.—Major axis 0.12 to 0.15, minor 0.1 to 0.12; pores 0.003 to 0.01, bars 0.003; main axis of the outer medullary shell 0.07 to 0.09, of the inner 0.03 to 0.04.

Habitat.—Fossil in the Tertiary rocks of Sicily; Grotte, Stöhr, Caltanisetta, Haeckel.

9. Prunulum pyrenium, n. sp.

Cortical shell very thick walled, smooth, with large irregular, roundish pores, three to four times as broad as the bars; six to eight on the half equator. The bottom of each funnel-like pore is closed by a thin siliceous membrane, perforated by three to five irregular roundish pores. Proportion of the two axes = 4 : 3. Both medullary shells ellipsoidal. (Closely resembles Stylatractus sethoporus, Pl. 17, figs. 2, 3, but is devoid of the polar spines.)

Dimensions.—Major axis 0.16, minor 0.12; pores 0.015 to 0.02, bars 0.005; porules 0.01; main axes of the medullary shells 0.07 and 0.03.

Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.

Definition.— with simple ellipsoidal cortical shell and double medullary shell, with numerous radial spines, but without polar tubes.

The genus Prunocarpus differs from Prunulum only in the radial spines of the cortical shell, and exhibits therefore the same relation to it that Druppocarpus bears to Druppula. While in the latter the medullary shell is simple, in the former it is double.

Definition.—Network of the cortical shell regular, with meshes of equal size and similar form.