140 PERMIAN FOSSILS. 



Cleiothyris pecUnifera, as British, is only known to occur in the shell-hmestone of 

 Humble ton Cluarry, where it is not common ; and in the Breccia of Tynemouth Chff, 

 where it is extremely scarce: the testiferous specimen represented in PI. X, figs. 1, 

 2, 3, 4, is the only one I have procured in the latter place. It is also a scarce 

 fossil in Germany ; since Dr. Geinitz records its occurrence in only two localities, 

 Milbitz and Corbusen in the under Zechstein. The Russian shells included in the 

 synonymy from de Verneuil, were found in the Permian marls of Kirilof, Tioplova 

 west of Arzamas, and Nikefur in Bielebei, Orenbourg. Count Keyserling records its 

 occurrence in Permian limestone on the Wol near Kischerma, and on the Wym near 

 Seregof, in Petschora-Land. 



Sub-class ANCYLOPODA, J. E. Gray. 



Diagnosis.- — "The oral arms recurved."^ 



This division is distinguished from its co-ordinate, Helidopoda, in having the labial 

 appendages or oral arms recurvedly folded, and not spirally twisted as in the latter, — 

 a difference which is in like manner participated by the apophyses of these organs. 



It will be recollected that certain groups of Helictopoda have their labial appendages 

 either entirely unsupported, or only slightly sustained by an apophysary system ; for 

 example, SarcicobracJda and Hypothyrida ; — probably the same may be predicated of 

 the Ancylopodous groups Mhynchorida and Aryiopida. 



Mr. Gray has divided the present sub-class into two orders, Ancylobrachia and 

 Cryptobraclda ; but for the reasons elsewhere given (vide ante, pp. 81-2.), it has been 

 deemed advisable to merge both into one, distinguishing it by the first appellation. 



Order Ancylobrachia, Gray. 



Diagnosis. — " The oral arms" in general " affixed to calcareous plates, forming hoops 

 attached to the hinge-margin of the ventral valve (dorsal, nobis), and prominent in its 

 cavity. - 



Having placed in the present order the families Argiopidce and Bhynchoridce, the 



1 Mr. Gray adds : "and affixed to fixed appendages on the disc of the ventral valve. SheU minutely 

 and closely perforated." (Vide Annals and Mag. of Nat. Hist., 2d series, vol. ii, p. 435.) In the next page 

 the following diagnosis is added : " The oral arms not extensile, or only at the tip ; on fixed shelly supports, 

 or in grooves in the under or ventral valve ; the mantle is adherent to the shell, the suhstance of the shell 

 being pierced with numerous minute perforations, which are pervaded by the processes of the mantle." I 

 have considered it best to leave out the foregoing in the text, as some Anchylopods appear to be without 

 shelly supports : as to the shell being perforated, this appears to be a character general in the Pallio- 

 branchs. 



2 Annals and Magazine of Natural History, 2d series, vol. ii, p. 435. 



