EARLY STAGES OF TEREBRATULINA. 



39 



Fig. 30. A stags slightly more advanced than the preceding. The lip is seen thrown back, disclosing the 

 capacious mouth. 



Fig. 31. Another view of the same opening. 



Fig. 32. A stage more advanced, in which the lophophore begins to assume the characters of the adult. 

 The cirri are now more numerous and more attenuated, and the lip is not so widely reflected. 



Figs. 33, 34. Showing the mouth of fig. 32 in different states of contraction. 



Figs. 35, 36, 37. Views of the mouth of an adult individual, showing oral tubercle, and oral groove. 



Fig. 38. Fragment of shell highly magnified, showing scales, tubules and outer layer, with lines of accre- 

 tion indicated by rows of flattened, bead-like nodules. 



Fig. 38, A. Exterior portion of tubule, showing radiating pores. 



Fig. 39. Single scale. 



Fig. 40. Single scale, broken across, and showing ridge in section. 



Fig. 41. Five scales in position. 



Fig. 42. Fragment of anterior portion of haemal valve. 



Fig. 43. Two scales from an adult specimen. 



Fig. 44. Portion of crural process from early stage. 



Fig. 45. Acicular scales from early stage. 



Fig. 46. Right crural process, from early stage. 



Fig. 47. Acicular scales from base of crural process of adult. 



Figs. 48, 49, 50, 51, 52, 53. Portions of haemal and neural valves of early stages showing development of 

 crura. 



Figs. 54, 55. Corresponding parts of adult, natural size. 



Figs. 56, 57, 58. Outlines representing different stages from extreme young to adult, fig. 58 being natural 

 size. 



NOTE. No means of measurement were at hand when the original studies were made. A Hue enclosed by 

 a circle indicates the entire length of the shell from which the parts were drawn. Where the size is not 

 indicated, it will be understood that the parts are from equally young stages, unless otherwise described in 

 the explanation of plates. 



EXPLANATION OF LETTERS ACCOMPANYING THE FIGURES. 



m, mouth. 



e, epistome. 

 ce, oesophagus. 

 a, stomach. 



c, cardia. 



t, intestine. 



f, faeces. 



vm, ventral mesentery. 



I, liver. 



h, hepatic cells. 



Off, oral groove. 



ot, oral tubercle. 



d, divaricator muscles. 



Ib, lateral gastro-parietal bands. 



p, peduncle. 



pa, point of attachment of peduncle. 



se, setae. 



cm, pallial caecum. 



t, cirn. 



g, granules passing to and fro from liver to intes- 

 tine. 



cr, crura. 



cl, calcareous loop. 



ex, external shell layer, of a chitinous nature. 



in, internal shell layer, of calcareous scales. 



cce, pallial caeca. 



hp, hinge plate. 



cp, cardinal process. 



ds, dental sockets. 



fo, foramen. 



te, teeth of shell. 



cs, calcareous spiculae. 



en, notch for pallial caeca. 



H, haemal valve. 



N, neural valve. 



