KKPTILIAN AOE. J UR A SSIC PE R I O D. 79 



FAMILY PTERIHLE. (Sec page 27.) 



SUBFAM 1 1. v I 'TKI ! 1 1 \jf}. (Sec page 28.) 



(IKS-US FIERI A, ScoroLi. 



*. /Vn,., S<-oroi.i, Introd. Hist. Nat. 1777 GRAY, Zool. Proceed. 1847, 199. Htm, Am. Jour. Scl. and ArU [2], 



XXXVII, l->;4, -J17. 

 Avicul.t (Ki.ni.t), BBPO (part), Hncyc. M6th. 1792, pi. 177. CCTIIB (part), Tab. Elem. 1798; Anat. Comp. 



1800 ; Regne An. 1817 LAMK. I'rodr. 1799 ; Syst. An. 1X01, 134 ; Phil. Zool. 1809, 318, &c. 

 Uaryaritiftra (sp.), Hmni. Has. Col. 1797, 44. 

 Pi*rt:,<i,,, I.ISCK, Beschr. Rost. 1807 (not BOLTBH, 1798). 

 U*innium, LtHK, ib. 



Anonica, OKKX, Handb. d. Zool. 1815 ; Natgsch. f. Schulen. 1815, 652. 

 Ptrlamaler (sp.), BCIIDM. En. 1817, 107. 

 Klym. irri(t, a wing. 

 /.'j-'ini/i. Mytilut Airuni/o, LIXH. 



Shell obliquely subovatc, or sub trigonal, fragile ; surface smooth, striated, costated 

 or subspinous often with imbricating marks of growth ; inequality of valves gene- 

 rally distinctly marked ; byssal sinus in the anterior margin of the right valve well 

 defined. Cardinal margin long, straight, and produced into more or less distinct 

 winjjs at the extremities the posterior wing being larger than the other. Hinge 

 \\itb usually one or two small cardinal teeth under the beak of each valve. 

 The (simple) pallial line represented by a row of minute irregular scars, extending 

 from the subcentral impression of the adductor muscle obliquely forward to the 

 small anterior muscular scar beneath the beaks. 



Amongst the numerous fossil species referred by various authors to this genus, 

 there are, in addition to the several types we believe to belong to clearly distinct 

 genera, others which differ sufficiently from the living typical species to constitute 

 at least well marked sections. It is not our purpose, nor have we the necessary 

 material at band, to attempt to define here all of these various subordinate groups, 

 though it becdmes necessary to notice one of those including a species with which we 

 have to deal. The section to which we allude may be designated as follows : 



Oxytomii, MERK. 



Shell differing from the typical forms of Ptrrin (= Avicula), In being less oblique, proportionally shorter, more 

 distinctly inequivalve, and usually more strongly costate particularly on the left valve, around the pallial 

 margins of which the cosUe are sometimes produced in tbe form of free spines. The byssal sinus of the 

 right valve is also much deeper aud more sharply defined than in the typical species of Pttria. 



Type Ai-icula Jfuntteri, GOLDF. Petref. Germ. II, pi. czzviii, 2 a, to A. 1 Also Includes A. cottata, MOBKIS & 

 LTCKTT, A. tliyilalu, and apparently Manoiit interUmigata, QPIXSTEDT, and A. cygnipa, PHILLIPS. 



This section forms a transition from the typical Avicula to the genus Eumicrotii, and seems to be mainly, If not 

 entirely, confined to the Jurassic rooks. 



The genus Pferia, or Avwula^ is so nearly related to the older extinct genus 

 Pterinia, that the two groups are generally confounded, where the hinge and in- 



1 Several species appear to have been confounded under the name A. Munsteri, by other authors. 

 We regard the particular form figured by Goldfuss as the type of the section Oxytoma. 



