REPORT ON THE DEEP-SEA KERATOSA. 27 



further observations prove the existence of such pores, then these Physemaria must be 

 united with our Ammolynthus, as the simplest forms of Ammoconiclae. 



Genus 1. Ammolynthus, 1 n. gen. 



Definition. — Animoconidas with simple, tubular or urceolate, unbranched body. 

 Distal end of the tubule with a simple opening (osculum). 



The genus Ammolynthus is of special interest, as the simplest of all Keratose sponges, 

 and as a prototype corresponding perfectly to Calcolynthus among the calcareous sponges. 

 I propose to retain the term Olynthus (first employed in my Monograph of the Calci- 

 spongia?, 1872) for the simplest tubular sponge-type without skeleton, and to use the 

 term Calcolynthus for those forms of Olynthus which produce calcareous spicules in 

 the mesodermal outer wall of the utricle, and Ammolynthus for those forms, the pseudo- 

 skeleton of which is composed of xenophya. The important embryonic stage of many 

 sponges, which corresponds to these mature Olynthus-iorms, may be called Olynthula, 

 and the corresponding hypothetical phylogenetic form — the probable common ancestral 

 form of all sponges — Archolynthus (— Archispongia). 



Two interesting species of Ammolynthus were found in the Challenger collection, 

 both representing a simple utricle of the typical Olynthus-iorm. The pseudo-skeleton 

 of the smaller form (Ammolynthus prototypus, PI. VIII. fig. 1) is siliceous, composed of 

 Radiolarian ooze ; that of the larger form (Ammolynthus haliphysema) is calcareous, 

 composed of Globigerina ooze. The former was better preserved, and exhibited not only 

 remnants of the flagellated entodermal epithelium, but also distinct eggs. 



Ammolynthus prototypus, n. sp. (PI. VIII. figs. lA-lC). 



Habitat— Central Pacific, Station 271 ; September 6, 1875 ; lat, 0° 33' S., long. 

 151° 34' W. ; depth, 2425 fathoms; bottom, Globigerina ooze, containing many 

 Radiolarians. 



Sponge urn-shaped or urceolate, representing a simple ovate utricle, which is fixed 

 by a slender cylindrical pedicle at the proximal end, and opens by a cylindrical proboscis 

 at the distal end. Pseudo-skeleton composed of siliceous shells of Radiolaria. 



Ammolynthus prototypus may be regarded as the simplest architype of a Keratose 

 sponge, corresponding to Calcolynthus among the Calcarea. 2 The utricular body has a 

 length of 6 to 10 mm., and in its middle widest portion a breadth of 1 to 1*2 mm. The 

 inferior or proximal half of the body is formed by a cylindrical pedicle 0"3 mm. in 

 diameter, which is fixed to the bottom by a broadened basal plate. The superior or 



1 Ammolynthus = Sandy fruit, uppos, ohvos. * Compare my Monograph, 1872, pi. i., vol. i., pp. 339, 342, etc. 



