FROM THE UPPER GREENSAND. 169 



solve. The geological record of the Cretaceous rocks where the Salenid^e abound 

 is not so imperfect as many assert, and connecting forms, if such ever really existed, 

 ought to be found somewhere in beds that are so often searched and so diligently worked 

 for the Palseontological treasures they contain. Notwithstanding all this investigation, 

 Goniophorus lunulatus still remains an isolated genus represented by a single species 

 among the Salenid^e. 



Genus — Salenia, Gray, 1835. 



Salenia, Agassiz, 1838. Salenia, Desor, 1858. Salenia, Cotteau, 1864. 



Test small, circular, moderately elevated, sides inflated, more or less convex above and 

 flat beneath ; poriferous zones narrow, pores unigeminal, simple in the zones, and crowded 

 near the peristome ; ambulacral areas narrow, gently flexuous, with two or four rows of 

 close-set homogeneous mammillated granules. Inter-ambulacral areas wide, with two 

 rows of large crenulated imperforate tubercles. 



Mouth-opening nearly two thirds the diameter of the test ; peristome divided into ten 

 unequal lobes by feeble incisions ; vent circular, periprocte elevated, excentral, and 

 posterior, placed at the right side of the axial line of the body ; apical disc shield-shaped, 

 covering a large portion of the dorsal surface ; plates prominent, with a deeply undulated 

 border; the ovarials and suranal large and pentagonal, the oculars wide and cordate ; the 

 sutures punctuated or incised, and the surface of the plates smooth in S. petalifera, 

 sometimes granulated, in S. granulosa, or striated with geometrical lines forming various 

 figures, as in 8. Clarkii and S. Austeni. 



The right antero-lateral ovarial plate exhibits a slight laceration, in which the madre- 

 poriform body is sometimes seen in well-preserved specimens ; often it is invisible. 



The spines are known only in a few species ; in some they are long, slender, and 

 aciculate ; in others they are stronger, with spatulate terminations (PI. XXXVIII, fig. 2) ; 

 some rarer specimens have their stems flexed, and others have the extremities bent to right 

 angles with the stem (PI. XXXVIII, fig. 3 ; PI. XLII, figs. 1, 2, 3, 4, 5). 



The genus Salenia is distinguished from Heterosalenia and Pseudosalenia by its 

 imperforate tubercles, and from Peltastes, which it very much resembles, by the position 

 of the vent. In Salenia the periprocte opens excentrically on the right side of a line passing 

 through the axis of the body, whilst in Peltastes the periprocte lies in the centre of such 

 an axial prolongation. 



22 



