Palceozoic Bivalved Entomostraca. 407 



P. umhilicata, P. valida, and their allies belong ; and the 

 ventral convexity, overhanging the margin, hides the con- 

 tinuous row of denticles which borders each valve. The sur- 

 face is reticulate except at the anterior end. The interior of 

 each valve has a thin cross wall in the anterior region, 

 dividing off about an eighth of the length of the valve from 

 the rest of the interior. This constitutes the generic distinc- 

 tion. The narrow crescentic area of surface, corresponding 

 to the separated portion of the interior, being destitute of 

 ornament and therefore smooth, gives the specific name. 



There are eight or nine individuals (from the soft shale- 

 beds of Frojel) among the specimens sent from Stockholm in 

 1886. 



It is correct to take the smooth end of Primitiopsis for the 

 anterior^ because that end has its analogue in the structure of 

 the recent Ghlamydotlieca^ Saussure, although in this living 

 form the partition of the anterior portion is not always so com- 

 plete, and its outside not so distinctly ditferentiated from the 

 rest of the surface, as m. our Palceozoic specimens. 



1*. Prhnitiopsis planifrons^ var. ventrosa, Jones. 

 (PL XXII. figs. 19 a, Idh, 19 c.) 



Primitiopsis planifrons, var. ventrosa, Jones, Silur. Ostrac. Gothland, 

 1887, p. 6. 



This is closely allied to the last described, but is remark- 

 able for the relative convexity of its ventral region, its less 

 height, and increased dorsal hollow, making it narrow-oblong 

 and subcylindrical in shape. 



Only one specimen occurred among those sent in 1886, 

 from Frojel. 



X. Entomis, Jones, 1861. 



(Ann. & Mag. Nat. Hist. ser. 4, vol. xi. 187.3, p. 413.) 



1. Entomis Lindstroemi, Jones. 

 (PI. XXII. figs. 16 «, 16&.) 



Entomis Lindstroimi, Jones, Siliu-. Ostrac, Gothland, 1887, p. 3. 



An Entomis closely related to others already known, but 

 distinct from them all. 



It is ovate-oblong ; rounded at the ends unequally, ellipti- 

 cally curved below, and nearly straight above. The sulcus 

 is straight and strong, a little in advance of the middle of the 

 valve. The hinder moiety of the valve is fully convex, steep 



28* 



