138 



others. These wrinkles break up the riblets into more or less 

 pronounced granules. The eves only slightly overhang. Slits 18, 

 at irregular distances. Margins of teeth are irregular, more 

 crenulate than pectinate. The strong pectination of its congener, 

 Loricella Angasi, Ad. and Ang., is quite absent, but the teeth 

 are deeply grooved to their bases, very little indication of this 

 being present in the living form. In L. Angasi a deep groove 

 runs from each slit to the apex. In the fossil under review there 

 is no groove, but its place is occupied by a slightly raised rib. 



Inside of Shell ( Articularnentum). — The valve^ except where 

 stained, is paler than the tegmentum, a rib running from each of 

 the slits to the apex, except that from the posterior slit, which is 

 almost parallel with the posterior margin of valve. 



Measurement. — Length, 16 mm.; breadth, 33 mm.; elevation, 

 7J mm. 



Locality. — Mornington. 



Remarks. — As compared with Loricella Angasi, the valve is 

 much flatter, is convex instead of concave. The coarse radial ribs, 

 nine or more in number, present in L. Angasi, are entirely 

 absent, the riblets being evenly distributed over the whole valve. 

 The largest specimen of L. Angasi known to us measures 68 mm. 

 by 44 mm. This valve is fully one-fourth larger than the anterior 

 valve of that specimen, and therefore we may conclude that when 

 living this ancient form would have measured fully 85 mm. by 

 55 mm. 



4. Plaxiphora eoncentpiea, n. sp. PL iv., fig. 8. 



One example of posterior valve only. 



General Appearance. — Broad, rounded. Color pale-brown, 

 slightly olivaceous. The tegmentum is posteriorly bent over, and 

 continued for some distance on the underside of shell. Mucro 

 evidently postmedian, though much worn. The anterior portion 

 of shell well preserved, showing six strong concentric ribs, each 

 following closely the contour of the margin of the shell. There 

 are evidences that these ribs were continued without any break 

 right round the posterior margin, though the ribbing in this part 

 of shell is less strong, and the ribs are closer together. No other 

 sculpture is discernible on the tegmentum. Insertion plates 

 unslit in the posterior valve. 



Measurement. — Posterior valve, total width 17 mm., total 

 length, 10 mm.; width of tegmentum only, 15 mm.; length of 

 tegmentum only, 7 mm. 



Inside. — Articuiamentum white, sinus 4 mm. wide at apex, 

 8 mm. at widest part. Sutural laminae produced beyond the 

 tegmentum, \^ mm. The sutural lamin?e and insertion plates 

 ^re remarkably posteriorly thickened. The two dorsal pits and 

 lateral grooves are very deep. 



