96 MOLLUSCA FROM THE GREAT OOLITE. 



the middle of the valves; anterior side rounded, posterior side elongated, the superior 

 border being nearly straight, and sloping obliquely, the posterior extremity is rather 

 truncated ; an obscure and obtuse angle descends obliquely upon the posterior side ; the 

 sides of the shell have a few irregular folds of growth ; the base is curved elliptically. 



A delicate species, which varies considerably in its figure, and in the distinctness of its 

 lines of growth ; the dental characters are minute, and can rarely be exposed. It is nearly 

 allied to a much larger and more stout Inferior Oolite species, in which the figure is usually 

 more elongated, and the dental characters much more conspicuous. The relative dimensions 

 in this shell vary so much that measurements have little value, but the umbones are always 

 anterior to the middle of the valves. It occurs rather commonly throughout the shelly 

 beds of the formation. 



Locality. Minchinhampton. 



QUENSTEDTIA. 



Testa (equivalvi, sub&quilaterd, oblongd et planatd ; umbonibus parvis, contiguis, com- 

 pressis ; ligamento externo ; foved ligamenti angustd et elongatd ; margine anlico rotunda, 

 postico compresso, subquadrato ; superficie plicis longitudinalibus plus minusve instructd. 

 Cardo dente cardinali unicd obtusd et transversd in valvd sinistrd, valva dextra fossa 

 cardinali unicd transversd sub umbone sitd. Impressiones musculares postici rotundi, antici 

 elongaii et sinuati ; impressio pattealis sinu brevi. 



Shell equivalve, subequilateral, oblong, and flattened ; umbones small, contiguous, and 

 compressed ; ligament external, placed in a narrow elongated groove ; anterior margin 

 rounder ; posterior margin compressed and subquadrate ; the surface with irregular longi- 

 tudinal plications more or less conspicuous. Hinge with one obtuse transverse cardinal 

 tooth in the left valve, which is received into a corresponding pit in the opposite valve. 

 Posterior muscular impressions rounded ; anterior impression elongated and sinuated ; 

 siphonal scar with a small sinus. (Tab. XV, fig. 12. Tab. IX, fig. 4. 6.) 



A genus approximated to Psammobia in the general figure of the valves, but dis- 

 tinguished from it in the position of the ligament, which is placed in a narrow fossa, 

 instead of upon the raised nymphal plate of Psammobia ; the single transverse tooth is 

 another distinctive feature, and reminds us of Myoconcha ; the sinus in the siphonal scar 

 is much smaller than in Psammobia or Sanguinolaria. 



QCENSTEDTIA oBLiTA, var. Tab. IX, fig. 4, 4<z, b., and Tab. XV, fig. 12. 



Syn. PULLASTRA OBLITA, Phillips. Geol. York., I, tab. 11, fig. 15. 



Testa ovato-oblongd compressd ; umbonibus parvis medianis ; antice rotundatd, postice 

 comprcssd, subtruncatd. angulo obliquo declivi obtuso ; latere postico plicis longitudinalibus 

 irregularibus. 



