137 



Choriplax grayi pattisoni, n. sub-sp. 



Differs from G. grayi, Ad. and Aug., in its greater width 

 and in the fact that the tegmentum is proportionately smaller. 

 The measurements of C. grayi, s.s., are quoted by Pilsbry 

 (I.e., pp. 21, 22), are: length, 13; width, 5 mm. Tegmentum, 

 li x If mm. Whereas the measurements of the present speci- 

 men are 18 x 8 h mm., and the tegmentum Hxl mm. 



An examination of the drawings made by E. A. Smith 

 and figured by Pilsbry (I.e., pi., figs 9-11) will further ex- 

 plain these differences. 



General Appearance. — Broadly oval, the posterior valve 

 being much larger than the anterior. The tegmentum reduced 

 to a small, heart-shaped, raised portion at the apex of each 

 valve, this portion being pink. The balance of the shell is 

 olive-green, due to an extension of the epidermal layer of 

 the girdle over the whole of each valve, with the exception 

 of the small, raised, heart-shaped tegmentum before referred 

 to. The epidermal skin is minutely granulose, semi-trans- 

 parent, and free from scales, hairs, or spicules. 



Colour. — The small, heart-shaped, exposed portions (or 

 tegmentum) are Prussian Red with flecking of Ochre Red 

 (Ridgway's Colour Standards, pi. xxvii.). The epidermal 

 covering of the highly developed articulamentum portions of 

 the shell is, in a good light, olive-lake, merging into Sac- 

 cardo's olive, in the shaded or overlapping portions of the 

 sutural laminae (I.e., pi. xxix.). The girdle is warm sepia, 

 or a little darker. 



Inside of Shell. — Transparent, pearly, and very highly 

 polished. The plates are so thin and delicate that none of 

 them are quite unbroken on the interior margins. The 

 anterior margin of the sutural laminae is almost straight, the 

 suture is reduced to a mere inward bend imperceptible in 

 several of the valves. 



Anterior Valve. — The small exposed portion is semi- 

 circular; the apex, which in this species corresponds with the 

 mucro of the tail valve, is pronounced and approximately 

 smooth, the superficial layer semitransparent, showing sub- 

 cutaneous dark and light streaks radiating from the mucro. 

 These may easily be mistaken for grooves and ridges. This 

 smooth area is produced anteriorly for fully one-third of the 

 width of the tegmentum. The balance of the valve is 

 sculptured with rather widely spaced granules. There seems 

 no consistent arrangement of these. The mucro is anterior 

 to the posterior margin of the tegmentum, and the posterior 

 lobes of the articulamentum unite behind same. 



Median Valves. — The small exposed tegmentum is 

 heart-shaped, posterior margin curved, in some straight, 



