248 UNITED STATES GEOLOGICAL SURVEY OE THE TERRITORIES. 



SAXICAVIDiE. 



t 



Genus GLYCIMERIS, Lamarck. 



Synoii. — Glicimeris (sp.), Klein (1753), Ostrac, 170 (not in accordance with the binomial system). 



Glycimeris, Lamarck (1799), Prodr., 83. — Gray (1847), Zool. Proceed., 189; and (1851), Brit. 



Aceph. and Brach., 62. — H. and A. Adams (1855), Gen. Kcccnt Moll., II, 350 (not Browne, 



1756, Humphrey, 1797, nor Stoliczka, 1870; not Glycymeris, Lam., 1801 and 1M09; 



uor Solium., 1817). 

 Panopea, Menard do la Groye (1807), Ann. du Mus., IX, 135. 

 Panopwa, Lamarck (1812), Ex.tr. d'uu Conrs, * * ; and (1818), Hist., V, 456; also of numerous 



others, but not H. and A. Adams, 1856, uor Stoliczka 1870. 



Etym. — ; foinit . sweet ; fiipic, a part or portion. 



Type. — Mya tflycimeris, Burn (=Panopea Faujasi, Menard de la Groye). 



Shell large, transversely oblong, with extremities gaping, and surface 

 concentrically furrowed and covered by an epidermis ; hinge with a single 

 cardinal tooth in each valve, fitting into a corresponding pit in the opposite 

 valve ; ligament attached to prominent external fulcra ; pallial impression 

 continuous, but provided with a deep posterior sinus. 



This genus is closely allied to Panomya, Gray (— Panopcea, H. and A. 

 Adams, 1856, = Glycimeris, Stoliczka, 1870), but differs in having the siphons 

 of the animal united quite to their free extremities, instead of being separated 

 at the ends. The shell is also generally thinner, and its pallial line differs in 

 being continuous instead of interrupted or broken up as in PanorUya, though 

 it is deeply sinuous in both. Slight differences are likewise observed in 

 the hinge-teeth of these genera. 



Owing to the fact that shells belonging to several genera of the Anati- 

 nidic, closely resembling this genus, are found in rocks of various ages, it is 

 difficult to ascertain its exact geological range. We frequently see species 

 referred to it, under the name Panopcea, even from the Palaeozoic rocks, par- 

 ticularly from the Carboniferous and Permian ; but, although some of these 

 shells very closely resemble this genus in form, the gaping of the valves, &c, 

 it is almost morally certain that none of them really belong even to the same 

 family. At least, all of them that I have had an opportunity to examine 

 differ from Glycimeris (— Panopcea of some) in being very thin shells, with 

 a minutely granular surface, and, so far as known, without hinge-teeth. 

 Hence, they fall into the genera Ckcenomya, Allorisma, and other groups. 

 The Triassic, Jurassic, and some of the so-called Cretaceous Panopseas also 



