Mr. J. Lycett on the genus Quenstedtia. 53 



Y.-^Notes on the genus Quenstedtia*. By John Lycett, Esq. 



This genus of Lamellibranchiate Conchifera, described in the 

 Great Oolite Monograph of the Palseontographical Society, was 

 founded upon two shells figured in Prof. Phillips's ' Geology 

 of Yorkshire,' under the names of Pullastra oblita and Fsam- 

 mobia Icevigata, the former of them being chosen as the type of 

 the genus. 



Of Pullastra oblita y I have succeeded in clearing and exposing 

 the hinge of each of the valves in many instances, and am per- 

 fectly conversant with its characters, which will be found correctly 

 described in the Monograph alluded to. The siphonal, pallial 

 and muscular scars were ascertained in a cast from the York- 

 shire Dogger, and upon the characters supplied by these satis- 

 factory materials the genus was founded. Specimens with the 

 test preserved, and which admit of the hinge characters being 

 exposed, are obtained in the upper portion of the Inferior Oolite 

 of the Cotteswolds ; a single young example of the species only 

 having been afforded by the Great Oolite of Minchinhampton. 

 In the Great Oolite Monograph it was stated to be allied to 

 Psammobia, but distinguished from it by the dental characters of 

 the hinge, and by the absence of an elevated nymphal plate to 

 sustain the ligament. The general resemblance which the aspect 

 of this shell presents to the Mactromya mactroides of Agassiz 

 had not been overlooked, but as the figures of Mactromya mac- 

 troides, in the ' Etudes critiques ' of that author, consist for the 

 most part only of casts, which afibrd no information respecting 

 the hinge, it was considered unadvisable to allude to the pro- 

 bable identity, as it was certain that Quenstedtia possessed no 

 affinity either with Mactra or with the family of the MyadcB, and 

 the shells of Phillips had priority as species. This supposed 

 identity of Quenstedtia oblita with the Mactromya mactroides of 

 Agassiz, has recently been fully confirmed in the publication by 

 M. Terquem of an elaborate work, with plates, entitled, ^ Obser- 

 vations sur les Etudes critiques des MoUusques fossiles, com- 

 prenant la Monographic des Myaires de M. Agassiz.' In this 

 work the author has figured and described the Mactromya mac- 

 troides-, the figures representing the shell and cast of the 

 interior under different aspects : upon the same plate (No. 5) are 

 placed figures of the recent Psammobia vespertina for comparison ; 

 the conclusion drawn by the author from this comparison is that 

 Mactromya mactroides is a Psammobia. It will be observed 

 that in these figures, the author has altogether omitted one of 

 the most essential points of comparison necessary to establish a 



* Read to the Cotteswold Club, Sept. 16, 1856. 



