94 PSEUDODIADEMA 



further into the ambiilacral areas ; the mouth-opening is circular, and the peristome nearly 

 equally lobed. 



J/finities and Differences. — Pseudodiademu ]\Ialbosi resembles some of the larger forms 

 of P. Bronyniarii, from the Grey Chalk of Folkestone, in the cabinet of my friend the 

 Rev. T. Wiltshire, and figured in PI. XX, fig. 2 a, h, in PL XXI b, fig. 3, and 

 PL XXI A, fig. 2. The tubercles in P. Bronrjniarti are not so numerous in each row; 

 the poriferous zones are narrower, and the bigeminal arrangement of the pores, so well 

 developed in P. Malbosi, is less distinct in P. Brongniarli. These certainly are nearly 

 aUied species, and require a careful examination to detect the small differences existing 

 between them. 



p. Malbosi resembles P. dubium, Gras, from the same horizon. I have only a mould 

 in plaster of the latter, not sufficiently sharp for scientific accuracy. 



Localitij and Stratigraphical Position. — 'Lhe specimens I have figured were collected 

 from the Lower Greensand at Whales Chine, Isle of Wight, in the Crioceras-beds that 

 pass across that chasm, associated with Ammonites Martini, D'Orb., Crioceras Boioer- 

 bankii. Sow., Gryplicea sinnata. Sow., &c. 



The specimens in the Museum of the Royal School of Mines were collected by Mr. 

 H. B. Mackeson, from the Lower Greensand (Kentish Rag) of Llythe, and presented by 

 him to that institution. Specimens are extremely rare in both the places cjuoted. 



The foreign /ocf//zY/r'.s, according to jM. Cotteau, are La Classe (Aude), Opoul (Pyrenees 

 Orientales), where it is abundant in the Upper Ncocomian beds, associated with Echino- 

 spatagws CoUegnii, D'Orlj. 



B. — Species from the Gault. 

 PsEUDor)iADEM.\ WiLTSHiREi, Wright, nov. sp. PL XVI, figs. 1 c— /, 2, 3. 



Test moderately large and equally depressed at both poles ; ambulacral areas wide, 

 with two rows of tubercles, large and approximated in the lower half of the area, small and 

 detached in the upper ; poriferous zones narrow, flexuous, pores in single file throughout ; 

 inter-ambulacral areas narrow, two roAvs of primary tubercles, and a few irregular 

 secondary tubercles at the base of the area, primaries large and approximated in the 

 lower half, small and remote above; miliary zone wide and finely granulated above, 

 narrow and with large granules below ; spines long and slender, the stem ornamented 

 with delicate longitudinal lines. 



Dimensions. — Height six tenths of an inch ; transverse diameter an inch and a half. 



Description. — We only possess a fragment of this beautifid form, still it has been 

 enough to enable Mr. Bone to give a restoration of the test in PL XVI, fig. 1 b. The body 

 is inflated at the sides, and nearly equally flattened on the upper and lower surface. The 



