i: i: PTILIAN AGE. J UR ASSI C PE RI OD. 103 



tab. 1832 ; ib. 756 ; again in LAM. 2d ed. VI, 63. F. A. ROBXEB, Vent. Ool. 1636, 126. BBO>. Leth. 

 7, Sh4. \.iAssii;, Ktu.I. frit. Mol. Fogs. 2d liv. 1842, 37. ttuttiT, 111. Cat. 1844, 1, 18, 4o. 4o. 

 iJumytra, KLEJII.V., Ili.-t. I'.rit. An. 1 828, 408 and 424. 

 t Cymella, MKEK, Siuitluoniau Clik. List Cret. FOM. 1S04, 34. 

 /.Vyw. /'A../.1S,- Mya. 

 Ty/it. P. Candida, SOWKBBT. 



Slicll (liin, equivalve, ]>carly within; longitudinally oblong, oval, or subtrigonal; 

 inequilateral and vrntricose; extremities usually both gaping, but the posterior 

 more widely than the other. Surface ornamented with radiating costa?, crossed by 

 < 'OIK -entrie striir, or uiorc or less distinct, sometimes nodular, ribs. Hinge with an 

 oli-< lire lamellar tooth, and a small triangular pit in each valve. Ligament short, 

 M;I!. 1'allial line and muscular impressions generally faintly marked; the 

 latter broadly sinuate. 



The animal of Pholailomya Candida, according to Owen, has its mantle provided 

 with four openings a pedal, a siphonal, and an anal aperture, with a fourth small 

 circular orifice at the under part of the siphons. The gills are thick and finely 

 plaited, the outer lamina being extended dorsally. The foot is provided with a 

 small accessor)' bifurcating appendage behind. 



Prof. Agassi/, who has produced the most important work on this genus, sepa- 

 rates the species into two principal sections, and again divides each of these into 

 several subordinate groups, as follows : 



SKTIOH I. Specie* Without a Circumscribed Cardinal Area, 



1. "IKuIticostata?," AGASSIS. 



Shell more or leas elongated ; radiating costn numerous, well defined. 

 Examples. /'. itmicoslnta and /'. nulticottata, Ao. (Jurassic and Cretaceout.) 



a. " TrigonataV AOASSII. 



Shell subtrigonal or more or legs oblong ; anterior side gibbons, often closed ; posterior more compressed and 

 distinctly gaping ; beaks generally elevated, sometimes perforate. Surface with distinct concentric ridges, 

 often extending npon the extremities of the valves, and crossed upon the flanks by well-defined tubercular 

 radiating cost*: cardinal area distinct, bnt not sharply defined. 



Examples. P. arcuata and P. nudn, Ao. (Cretaceous, Tertiary, and Recent.) 



3. "Bucardinac," AOASSIZ. 



Shell snbtrigonal, or more or less ovoid, gibbous, and comparatively thick ; truncated, somewhat gaping, 

 and usually flattened anteriorly; posterior side distinctly gaping; beaks gibbons and closely contiguous. 

 Surface with strong, often tubercular radiating cosUe on the flanks ; muscular and pallial impressions 

 distinct. 



Ezampltt. P. cincta and P. decuuata, AOASSIZ. (Liat to Tertiary.) 



SECTION II. Specie* With a Circumscribed Cardinal Area. 



4. "Flabellatap," AOAMB. 



Shell usually much elongated ; radiating costs prominent and often distant, generally confined to the flanks. 



General aspect similar to the " Alulticostata," bnt differing in the possession of a defined cardinal area. 

 Examples. P. pelagica and P. timilit, AOASSIZ. (Jurassic.) 



5. "Ovales," AOASSII. 



Shell ovoid, more or less compressed ; one or the other of the extremities gaping : cardinal area sometimes 



not very distinct behind ; cost* linear, often orenate. 

 Example*. P. tenuicostata and P. pectinata, AGASSI*. (Jurassic.) 



6. "Cardissoldes," AOASBII. 



Shell snbtrigonal, similar to the " Bucardina" of the first principal division, bnt differing in the possession 



of a defined cardinal area, and in having the cosUe lee* numerous and more faintly marked. 

 Examples. P. cancel lata and P. cardiaoidet, AGASSIS. (Jurauic.) 



, 



