1917.] NATURAL SCIENCES OF PHILADELPHIA. 201 



developed in both valves. Sculpture of sharp, low, thread-like eon- 

 centric lamellae without interstitial striae. 



Length 31, alt. 22.5, diam. about 11 mm. 



Both of these species of Semele are apparently from the Orlhaulax 

 bed, having the same hard matrix. They stand close to Ballast 

 Point species, yet are evidently distinct. 



Tellina (Merisca) errati n. sp. 



Tellidora crystallina Chemn., Gabb, Trans. Amer. Philos. Soc, XV, 1873, p. 

 249. 



The shell is compressed, with nearly median beaks, the dorsal 

 slopes on either side straight. Anterior end broadly rounded, 

 posterior end acute; lower margin strongly arched, a little incurved 

 near the posterior end. The right valve has an angular ridge below 

 the posterior upper margin, followed by a radial concavity. Left 

 valve with a slight concavity below the same margin. The surface 

 is matt, with sculpture of delicate, regularly and rather widely 

 spaced laminar concentric ribs. In the intervals there is very fine 

 radial crinkling, the wrinkles partly converging upwards into many 

 little groups. The pallial sinus extends nearly to the anterior 

 adductor scar, and is concrescent below with the pallial line. Lateral 

 teeth well developed in the right, wanting in the left valve. 



Length 13, alt. 9, diam. of left valve 2 mm. 



Type No. 2666, A. N. S. P. 



Gabb's identification of this species was really remarkable. There 

 are two left valves and a ])roken right valve, the latter larger, indi- 

 cating a length o^" 17 or 18 mm. 



Metis eiferta u. sp. 



The beaks are nearly central, left valve more convex, being plump 

 throughout, right valve plump anteriorly, then broadly concave, 

 strongly angular posteriorly. Surface very lightly striate with 

 periodic marks of growth-arrest, and on the anterior and posterior 

 areas there are fine laminae like those of M. chipolana. Radial 

 striation is fine and superficial. 



Length 36, alt. 30.7, diam. 17 mm. 



Type No. 2665, A. N. S. P. 



Related to M. chipolana, but readily distinguishable by the much 

 plumper form, broader and deeper concavity of the right valve, and 

 presence of little laminae only on the ends. The valves are slightly 

 skewed. If evenly placed the diameter would be about 18 mm. 



