984. SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Pedicle interior with long, slender teeth and deep delthyrial cavity; dental 
plates receding, flaring laterally and attached to the sides; muscles attached to 
a thin horizontal plate laid across the delthyrial cavity at the base of the dental 
plates and attached to the sides of the valve to leave a deep delthyrial chamber 
between the plate and the valve floor. Muscle scars well impressed on plate; 
adjustor-diductor scars located at base of dental plates; adductor (?) scars 
broad, occupying median region and separated from other scars by low ridges. 
Brachial valve with small, deep sockets defined by a fulcral plate; notothyrial 
cavity formed by brachiophore plates uniting with a median septum and the 
valve floor; brachiophores long and slender ; cardinal process located at the end 
of a low septum occupying the floor of the notothyrial chamber and with a bul- 
bous myophore; median septum thin, elevated anteriorly but not reaching the 
front margin. 
Genotype.—Elasmothyris concinnula Cooper, new species. 
Discussion.—This interesting little shell is characterized externally by con- 
siderable depth in both valves, costellate ornamentation, and a general resem- 
blance to Skenidioides. The interior, however, is marked by normal dental plates 
and a horizontal muscle plate in the pedicle valve, and a notothyrial chamber and 
long, slender brachiophores in the brachial valve. Besides these features the 
shell substance is punctate. 
Several characters of this peculiar genus need explanation. The determination 
of the presence of punctae rests on observation of silicified shells. This is not 
ordinarily a type of preservation that yields good evidence of these important 
structures, but in this instance nearly every specimen shows small black spots 
on both sides of the shell, some of which are radially arranged. These are taken 
to be fillings of punctae by mud, pyrite, or other impurity. Confirmation of the 
punctate condition is to be seen also in the structures of the brachial valve which 
are discussed below. The absence of a deltidium in such an early brachiopod is 
negative evidence. 
The pedicle valve is characterized by strong, sharp teeth buttressed by reced- 
ing dental plates which flare laterally and are attached to the sides of the valve. 
The plates are normal in every respect, but at their base a plate is built hori- 
zontally across the delthyrial chamber. This plate divides the delthyrial cavity 
into an upper and lower chamber. The plate is also marked by 2 oblique ridges 
that clearly indicate the position of muscle scars. 
At the base of the dental plates is an elongate, tear-shaped scar than can be 
interpreted in two ways: it is the adjustor scar which is usually found in that 
situation, or it is a scar of the diductor and adjustor muscles with no evidence 
left on the shell by which the individual scars may be differentiated. On this in- 
terpretation the adductor field is fairly large but no individual scars can be differ- 
entiated. The horizontal plate is somewhat variable in form. In some specimens 
it is horizontal and nearly flat. In others it is bowed medially in the direction of 
the brachial valve. This plate sets Elasmothyris quite apart from any of the other 
skenidioid shells such as Skenidioides, Tropidothyris, or Skenidium. 
The brachial valve of Elasmothyris suggests that of the punctate shell Lino- 
