55 



the lens its surface is seen to be minutely and concentricalh' riblied, the 

 ribs following the general outline of the shell. 



Length, three and-a-half lines ; greatest height about two and-a-half 

 lines ; maximum width (or thickness) about equal to the height. 



A single specimen, bmTowing into fossil wood. 



The solitary example from which the above description was made, is 

 both imperfect and immature. At jjresent it is not known whether the 

 anterior hiatus was permanently open or closed in the adult by a calca- 

 reous secretion. Not a vestige of any of the accessor}^ plates remains, and 

 their number, shape and position have yet to be ascertained. The 

 generic position of the shell can, therefore, only be inferred by analogy, 

 and that in a very vague and unsatisfactor}- way at best. 



The somewhat elongated shape, coupled with other characters, indicate 

 that the species should be referred to the Pholadinaj rather than to the 

 Teredina\ and its relations are apparently either with Martesia or Para- 

 fholas. The essential distinction between these genera is that in 

 Parapholas the umbonal accessory valve is " longitudinally divided in 

 two," while in Martesia it is single and entire. Stoliczka* is of opinion 

 that " the distinction scarcel}' deserves to be regarded of generic value." 

 Woodwardf defines the genus Parajiholas briefly thus, "valves with two 

 radiating furrows." Stoliczka| says " the two furrows running from the 

 um bones towards the periphery are said to be present in all known species 

 of Paraplwlas,'' and a part of Tryon's diagnosis of the genus § is, " surface 

 impressed by two oblique sulci, extending from the beaks to the margins." 

 Conrad's genus Pa?'apholas was proposed by him in 1849, and the type 

 species is admitted to be the Phohis Californica of the same author, which 

 has only one groove on each valve ! fn describing that species the 

 writer says, "valves much contracted suljuiediallj", with an oblique 

 groove." Chenu accordingly calls P. Californica a Martesia and not a 

 Parapholas. 



Tryon, whose monograph on the recent Pholadacea) (in the " Pro- 

 ceedings of the Academy of Natural Sciences of Philadelphia for 1862 ") 

 has done so much to clear up the confused synonymy of the group, 

 makes no reference to the fossil species. As he includes several forms, 

 (such as the Californian Pholas calva of Sowerby) which have two 

 oblique furrows on each valve, in Leach's genus Martesia as recently 



* " Cretaceous Pelecypoda of Southern India," page 24. t " Manual of the MoOusca." pagre 329. 



t " Cretaceous Pelecypoda of Southern India," page 24. 



§ " Proceedings of the Academy of Natural Sciences. Philadelphia, 18G2," iiajfe 194, 



