DESCRIPTION OF GENERA AND SPECIES. 



Family I. Ammoconid^e, n. fam. (PI. VIII.). 



Definition. — Keratosa without spongin-fibres. Pseudo-skeleton composed of xenophya 

 (or manifold foreign bodies), which are disposed in the thin malthar plate of the porous 

 tubular body. Canal-system tubular, developed on the Asconal-type (similar to that of 

 the Asconidse). 



The new family Ammoconidse, represented in the Challenger collection by three 

 different deep-sea genera, is of extraordinary morphological interest, for it is the first 

 example of a simple so-called "homocoelous structure" among the " Non-calcarea," viz., 

 that most remarkable organisation which is represented by the Asconidse among the 

 Calcarea. In the first genus, Ammolynthus, the body is a simple, unbranched tubule, with 

 an oscular opening at the superior end, opposite to the inferior pedicle (PI. VIII. figs. 1, 

 2) ; it corresponds to Calcolynthus among the Calcarea. The second genus, Ammosolenia, 

 is a branched or arborescent body, composed of several Ammolynthus (PI. VIII. fig. 3), 

 similar to Soleniscus. The third genus, Ammoconia, forms a loose, roundish framework, 

 composed of anastomosing tubules, without oscula, similar to Auloplegma (PI. VIII. 

 figs. 4, 5). The thin wall of all these tubular sponges is pierced by simple pores, through 

 which the water enters into the simple gastral cavity ; it issues either through these or 

 through larger openings (oscula). Remains of the entodermal flagellated epithelium lining 

 the inside of the tubes were visible in two genera examined, but no trace of an exodermal 

 pavement-epithelium was visible on the outside ; it was probably lost, as usual in spirit 

 specimens. The main mass of the thin wall is formed by foreign bodies, or manifold 

 xenophya, Radiolaria, Foraminifera, sand-grains, &c. They are connected by a 

 relatively scarce maltha, or a homogeneous ground-mass, in which the small cells of the 

 connective tissue are recognisable between the xenophya. 



Xenophya. — The foreign bodies which compose the pseudo-skeleton of the Ammo- 

 conidse, and which are cemented together by the scanty maltha of the mesoderm, are 

 calcareous in three of the five species examined — shells and fragments of Globigerina and 

 allied Foraminifera (PL VIII. figs. 2-4). They are siliceous in the two remaining species, 

 Radiolarian tests in one (fig. 1), spicules of siliceous sponges and volcanic mineral particles, 



