Palaeontological Speculations —Gratacap. 293 
support, because of interference with its axial extension. Dr. 
Beecher under “Genesis of Form,” says: “The principal char- 
acters shared by the two valves are the general outline and the 
hinge. In typical and generalized forms, as Lingula, Tere- 
bratulina, Cistella, and Discinisca, considered as before in re- 
gard to length of pedicle, freedom of movement, and direc- 
tion of longitudinal axis to the object of support, we find a 
key to these types of structure. In the individual development 
of Terebratulina, as shown by Morse, we first have the early 
embryonic shell (protegulum) with a short pedicle and 
straight hinge. The next stage retains both these characters, 
but the valves have become more unequal and the pedicle 
opening confined to the fissure of one valve. The result is a 
shell very much like Argiope or Megerlia (Megathyris and 
Muhlfeldtia), to which professor Morse also called attention. 
The same author next showed that the succeeding stage had 
a comparatively long pedicle, and a shell linguloid in form. 
Afterwards the defining of the pedicle opening, shortening of 
the pedicle and truncation of the neutral beak produced the 
final characteristic external features of Terebratulina. The 
deduction from this example and from Lingula is, that genera 
having pedicles sufficiently long to admit of freedom of axial 
movement have elongate and rostrate shells. The shortening 
of the pedicle brings the posterior part of the shell in more or 
less close proximity to the object of support, and, as growth 
cannot take place in that direction, it increases laterally, re- 
sulting in broader forms with extended hinge areas, as in many 
species of Cistella, Scenidium, Muhlfeldtia, Terebratella, 
Kraussina, etc.” 
If this is true it might be anticipated that a shortening of 
the pedicle would he attended with some slight widening of 
the shell at the beaks. It does not seem to be. Lingula mur- 
phyana King, is a long shell with a long pedicle; L. hiaiis, 
- Swains, has a shorter pedicle but structurally is an identical 
shell with murphyana; Lingula anatina is a broad shell short 
peduncled but retains the usual linguloid character of the 
beaks ; L. ovalis Rv. is a small narrow shell with short pedicle. 
In none of these forms of course is there any or very slight. 
suggestion of hinge areas, and there is no more suggestion of 
a hinge area in the short pedicled than in the long pedicled 
