286 PALAEONTOLOGY OF NEW YORK. 
ments. The foramen, dental plates and teeth are obsolete or obsolescent in the 
Devonian species.* 
In the brachial valve the delthyrium is also usually closed; the cardinal 
apophyses are strongly arched into the uinbonal cavity of the opposite valve, 
their surfaces of attachment being sometimes nearly parallel to the plane of 
the cardinal area of the brachial valve, and often extending beyond it. Small 
crural plates are always present, though they could not have been functional 
at maturity. Muscular arrangement similar to that of Leptcena rhomboidalis and 
Rafinesquina alternatei, the posterior scars being more elongate, the anterior pair 
usually less defined, and all the scars frequently obscured. The anterior 
muscular fulcra are sometimes developed into very prominent elongate apo¬ 
physes. The median septum often becomes elevated into a high crest at the 
center of the valve. Over the pallial region the interior of both valves is 
strongly papillose. External surface covered with radiating, sometimes fas¬ 
ciculate striae; rarely smooth. Shell-substance fibrous, coarsely punctate. 
Type, Leptcena demissa, Conrad. Hamilton group. 
Observations. The distinctive characters of this genus are clearly evident, 
but notwithstanding its importance, both zoologically and geologically, it has 
never been accorded general recognition except among American writers. Mr. 
Billings would not admit its validity; Dr. Davidson barely noticed the term; 
Professor Kayser and the German writers generally continue to refer its species 
to Stropiiomena (= Strophomena, Leptcena, Rafinesquina, etc.); Dr. (Ehlert 
has adopted it, making it a sub-genus of Strophomena, Rafinesque (de Blain- 
ville), while he proposes a new genus, Douvillina, which is essentially synony¬ 
mous. The genus Stropheodonta is a large one, being represented in American 
faunas by not less than fifty species, and it is emphatically characteristic of the 
Devonian. It makes its first appearance in the Clinton group, having a sparse 
representation in the Niagara, but becomes more abundant in the Lower 
* The obliteration of these parts may be due to the excessive secretion of calcareous matter in the uin¬ 
bonal region. Where this deposit is less there remains some evidence of these features, as in S. profunda of 
the Niagara, /S'. BecM of the Lower Helderberg, and especially in /S'. magnifica of the Oriskany sandstone, 
one of the largest species of the genus, in which the short dental lamellae converge and unite at the bottom 
of the rostral cavity, making a sort of pedicle-pit and leaving the delthyrium open. See Plate XIII, fig. 28. 
