ANIMALS. 13 



{Lymnorea mammillosa, Lamouroux), but it does not display the large oscula on the 

 summit of the mammillse, characteristic of the latter. The want of large excurrent 

 openings in this species has caused its removal from the genus Manon, in which it 

 was formerly placed. 



Mammillopora mammillaris occurs sparingly in the Shelly Limestone at Humbleton 

 Hill. 



Genus Tragos, Schweigger. 



Diagnosis. — '' Stirps e fibris densis, subgelatinosis ; superficies ostiohs distinctis."^ 

 (Schweigger.) 



The type of this genus is the Alcyonium incrustans of Esper, which belongs to the 

 order Halinida. There is considerable doubt as to whether the following two Sponges 

 ought to be placed in it. 



Tragos Tunstallensis, King. Plate II, fig. 5. 



Diagnosis. — Form irregularly infundibular. Summit expanded and slightly exca- 

 vated. Margin of the cavity irregularly lobed. Outer surface uneven. Substance fibrous, 

 with numerous, small, excurrent passages. 



The usual size of this Sponge is half an inch in height, and three quarters in 

 width. In its fibrous texture it resembles the Tragos patella^ figured by Bronn in the 

 ' Lethaea Geognostica,' pi. xvi, fig. 3. 



It is occasionally found in the Shelly Magnesian Limestone at Tunstall Hill. 



Tragos Binneyi, King. Plate II, fig. 6. 



Diagnosis. — Infundibuliform ; slightly excavated at the summit. Surface porous, 

 and irregularly tuberculated. 



This is a larger species than the last, occasionally measuring an inch and a half in 

 width, and two inches in height. It appears to have been variable in its relative 

 proportions, as some specimens are much less in height than in width ; they have 

 somewhat the appearance, however, of having been depressed by superincumbent 

 pressure. None of the specimens examined show any excurrent openings on the 

 outside, but it is suspected that these, as in many recent cup-shaped Sponges, were 

 situated within the cavity : this part, however, is in general so filled up with mineral 

 matter and casts of shells, that it is impossible to offer any decided opinion on this 

 point. Where the outside is pretty clear of the investing mineral matter, there may 

 be seen a few small pores, which, it may be safely concluded, were the openings of the 



^ Handbuch der Naturgeschichte der Skelettlosen ungegliederten Thiere, p. 422, 1820. 



