278 CRETACEOUS PELECYPODA 



15. Aslarle, Sowerby, 1817, fCrassina, Lam., 1818). Shell sub-trigonal 

 or sub-orbicular, \\ii\\ attenuated, pointed, approached beaks ; surface concentrically 

 striated or laminated, hinge with three cardinal teeth in each valve ; in the riglit 

 the anterior and posterior are very small ; in the left valve the median and 

 sometimes posterior are large, and the anterior is sometimes only indicated, as 

 well as a lateral tooth, situated just above the muscular impression; ligament 

 long, generally lodged in a depression and supported by fulcra ; muscular impres- 

 sions rounded, or ovate, deep ; internal margin of shell smooth or erenulated. 



The first authentic specimens of Astm^te appear with the mesozoic period 

 and continue uj) to the present time, being mostly found in northern seas. 



Mr. Conrad (Am. Journ. Conch., v, p. 46,) suggests that Sowerby's oolitic 

 type species Astarte hirida is generically distinct from the recent northern forms 

 which Lamarck called Crassma. I have compared this type sjiecies also with 

 recent Astarte, and I find that in some of the more oval species there is also a 

 thickening of the anterior lunular margin in the right valve, as noted in the 

 fossil lurida. I do not think that they could be on that account generically 

 sej)arated, though I admit that there are probably several other genera represented 

 among the fossil species which we call Astarte; I would particulai'ly allude to 

 Erlphyla, Grotriania, and Myrtea, a sub-genus of Lucina. Very closely allied to 

 the last, if not identically the same, is Conrad's Lirodiscus. 



15 a. Gonilia, Stol., 1870. Shell orbicular, small, hinge with three distinct 

 cardinal teeth in each valve, surface with angular striae, no epidermis ; type, 

 Xiticina ? (or Astarte) blpartita, Philippi, (Abbild. and Besch. Conch., vol. ii, 

 ^ster^e, pi. 1, fig. 9 ; non ^. hipartita, Soav.). The round, rather Luc'moid form 

 and the angular striation of the surface indicates in this species a distinct 

 section of Astarte, similar to Cyclas, a sub-gen. of Lucina. 



16. Grotriania, Speyer, 1860, (Zeitsch. d. deutsch. Geol. Gesellsch., vol. xii, 

 p. 496). Shell roundish, moderately compressed, conceiitrically sulcated or striated, 

 kinula and area very deeply excavated ; beaks produced and pointed, hinge with 

 two or more (often three) cardinal teeth in the right and two in the left valve, 

 the middle tooth in the former and the anterior in the latter being the strongest ; 

 each valve with a rib-like marginal lateral tooth on either side, accompanied by 

 a groove, muscular impressions oval, moderately excavated, internal margin finely 

 crenated. Type, Grot, seinicostatu, Speyer, from the oligoca^ne beds of Soellingen. 

 One species also occurs in the South Indian cretaceous rocks. 



This genus greatly resembles in external form an Astarte, but is readily 

 distinguished from it by the presence of the peculiarly elongated lateral teeth and 

 the deep kmula and area. The cardinal teeth equally easily distinguish the genus 

 ivom. Erlphyla, Gabb, ( vosiNiiisr^J, iuAvhich the pallial line is truncate posteriorly, 

 or more or less distinctly sinuated. 



17. PrcBconia, Stol., 1870. Oval, elongated, solid, veiy inequilateral, beaks 

 sub-anterior, approached, incurved, surface concentrically lamellated or striated ; 

 muscular impressions strong ; hinge with two cardinal teeth in the left and three 



