BRAoHIOPODA. 759 
The character of the muscular impressions is of greater impor- 
tance; the broad scars of the diductors in the pedicle-valve 
are here reduced to very narrow dimensions, are scarcely 
depressed and frequently not defined, but represented only by a 
radiate marking of the shell. In the brachial valve the adductor 
scars are two narrow impressions which widen anteriorly but are 
not divided transversely. The surface of the shell was covered 
with very fine concentric lines and the epidermal layer, which is 
usually effaced, was minutely punctate. Faint lateral plications 
are sometimes visible. 
These differences from the normal type of Srrrirer have led 
many writers to adopt McCuy’s term Marrinta for S. glaber and 
its allies. It is evident, however, that this division of the smooth- 
shelled species embraces more than one subordinate type of 
structure; they may be divided into 
1. Aseptati (— Marrinia, McCoy, 1844). Shells in which dental 
lamelle and septa are wanting. 
(S. Maia, Billings, Corniferous limestone; S. subwmbona, Hall, 
Hamilton group; S. glaber, Martin, Coal Measures.) 
2. Septati. Shells in which dental plates or septa are well 
developed. Two groups of the septate Glabratimay be recognized: 
(a) Marrrntorsis, Waagen, 1883. Species with the lamellz 
developed in both valves. 
(IL. inflata and 1. subpentagonalis, Waagen, from the Productus 
limestone of India). 
(b) (Gen. nov.,” Tschernyschew, = MenrzEeiia, Quenstedt, 
1871(¢)), Type of Martinia semiplana, Waagen. Shells with dental 
lamellz scarcely developed, but with a prominent median septum 
in pedicle-valve. Menrzeria was founded upon the Spiifer 
medianus of the Muschelkalk. 
Subgenus Cyrtia, Dalman. 1828. 
(Plate 29, figs. 4-11.) 
Shells like Srrrirmr but having a high vertical cardinal area 
and semi-pyramidal contour. 
(Type, C. exporrecta, Wahlenberg. Silurian-Devonian.) 
Cyrria is the designation of a group, having a meager repre- 
sentation and slight morphological value. 
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