24 MOLLUSCA FROM THE CRAG. 



its superior extremity extended in the form of an elongated and very narrow canal ; 

 base with sometimes a lengthened siphonal canal, and a sinus in the lower part of 

 the outer lip. 



RosTELLAEiA PLIKIMACOSTA. 5. TFoocl. Catalogue of Crag Shells, 1842. 

 A few worn specimens of a species of Rostellaria are in my cabinet, from the Red 

 Crag of Sutton. They are in a mutilated condition, and unfit for fair comparison ; they 

 bear a resemblance, and may possibly be the B. Imida, J. Sow. (Min. Con. t. 7), 

 perhaps washed out of the London clay. 



Aporrhais,* Aldrovandus. 

 Rostellaria. Lam. 1801. 

 Chenopus. Phil. 1836. 



Gen. Char. Shell turreted or fusiform, thick and strong, generally ribbed, nodulous, 

 or carinated ; aperture ovate or elongate, terminating in a canal with a calcareous 

 pointed process at the base, and having, in the adult state, an expanded, angularly 

 lobed, or digitated outer lip, sinuated at the lower part near the canal. Operculum 

 corneous. 



The name for this genus was used by Aldrovandus in 1623, and by Petiver in 

 1 702, when describing the jies-pdicani with the following words : " Aporrhais Edin- 

 burgensis minor nodosa." (Gazophylacium, fol. 17, Tab. 79, f. 6, and Tab. 127, f. 11, 

 Cat. No. 85.) Da Costa (History of British Shells, 4to, 1778) characterizes the 

 same species under the name of Aporrhais with a new specific appellation, and a 

 reference to Petiver. In the ' Philosophical Transactions' for 1 823, Dillwyn uses the same 

 name as a generic term, and applies it to the j)es-pelicani ; and this may be considered 

 as a fair revival of a name proposed before the time of Linnaeus. This species, upon 

 which the genus has been established, was included by Lamarck in Rostellaria, in 

 consequence of the sinus in the lower part of the outer lip resembling the shells of that 

 genus. 



In 1836, M. Philippi (Enum. Moll. Sic. vol. i, p. 215,) described the animal of 

 pes-pelicani, which, he says, is decidedly different from that of Rostellaria, and proposes, 

 in consequence, to erect it into a genus, under the new name Chenopus, with thejoes- 

 jieUcajii as its type. 



It has been contended that the genus was in the first instance established upon 

 the form of the shell alone, without a knowledge of its animal inhabitant ; and that a 

 detection of a difference in some of the soft parts, with a publication of the anatomical 

 details, will justify the rejection of an old established name and the substitution of a 

 new one. A principle which, if admitted, will endanger the stability of many other 

 genera that have been formed upon the shell alone, and priority of date, as now 

 considered, will be no security for an author's name. 



* Probably derived from atrop/aa? or oTrop/Wj, rent, torn, in allusion to tbe ragged or digitiform 

 processes of tlie outer lip. 



