l.'M AxNALs OF THE Carne(;ie Museum. 



valves are subetiually convex, the ventral valve a little the deeper. 

 The dorsal valve is elongate oval, .87 mm. long and .84 mm. wide, 

 while the ventral valve has a narrow rostrate beak which extends . 2 

 mm. back beyond the 'hinge. The delthyrium is large, triangular 

 and without deltidial plates (Fig. 33). The loop of this specimen 

 can not be determined as only a short portion is retained. On the 

 dorsal beak the first punctae can be seen and their arrangement agrees 

 with that seen on the nepionic shell of Terebratitlina septenirionalis.^ 



Fig. 33. Eutic'Ha /inckiccni llaW. Young specimen with open delthyrium. X 16. 

 Fig. 34. The same species. An adult, showing several growth stages. XS- 



The first pair of punctre are .072 mm. from the beak and in front of 

 them, on the median line, and .109 mm. from the beak, is a third 

 one. Beyond this they are scattered sparingly o\er the surface for a 

 short distance but toward the front of the shell they become very 

 numerous. 



Changes During De'velopinent. 



Outline. — The outline changes very little during the various stages. 

 There are both broad and narrow forms. The index of the ventral 

 valve varies from .68 to .88 in young specimens and from .76 to .92 

 in adults. The dorsal valves of adults of the broad type are nearly cir- 

 cular, while the index of the same valves in the narrow form is from 

 .71 to .88. 



Convexity of Valves. — In young stages the ventral valve is slightly 

 deeper than the dorsal, but in the adult the convexity of the valves is 

 often reversed. The ventral beak extends straight beyond the hinge 

 in young individuals. In adults the umbo is incurved and the apex 

 of the beak is truncated by the pedicle opening. 



'E. S. Morse, Alemoirs tioston Sor. A'af. //is/., \'ol. V. No. 8, 1902, pi. 62, fig. 

 15, al.so A/ei>i. Bos. Soc. iVa/. //ist., Vol. II, pt. I, No. 2, pi. I, fig. 3. 



