268 TF. D. Lang — On Stomatopova antiqua. 



stability in the evolving form. To have definitely named such 

 evolutionary stations would have implied a complete knowledge of 

 the evolution of the group. But as each point in the series was 

 independently met with, so it was described and named, and its 

 connection with other points discovered later. In the supposed case 

 where this has been done, more than two species would occasionally 

 be found in one unbranched series. It might be said that the names 

 of the middle species, that is, those that lay along one branch 

 between two bifurcations, were useless and might be discarded, or, 

 being only mutations, might be named as such. This, however, 

 would be a pity, for reference marks are needed along an unbroken 

 series. Moreover, since the superfluous names are thus treated as 

 synonyms, the question of priority is at once raised. Therefore 

 it seems advisable in such a case to keep the intermediate names. 

 But where, as in the species described in this paper, slight, hitherto 

 unnamed differences occur as the form passes from zone to zone, the 

 forms could be named as mutations, like those above, in order not 

 unduly to multiply ' species,' The original difficulty, namely, to 

 sa3' where the mutations of one species end and those of another 

 begin, could be solved conventionally by taking the first stratigraphical 

 boundary below the higher species. And if it be objected that such 

 a division is purely conventional, it may be answered that it is 

 chosen no more arbitrarily than is the point in the series from which 

 the individuals comprising a species were taken. With complete 

 knowledge specific boundaries must be conventional. And all the 

 difficulties in nomenclature arise from the inadequacy of the system 

 now in use, which seeks to bind within rigid systematic limits the 

 phases of series which are in a perpetual state of flux. 



EXPLANATION OF PLATE XIV, p. 264. 



Fig. 1. — D. 7539. Stomatopova antiqua, Haime, mut. capricornensis, encrusting 



Montl'naltia Victories, Duncan. Middle Lias : zone of Z. capricornus, 



? Cherrington, "Warwickshire, x about 12. 

 ,, 2. — D. 7620, zoariura 2. Stomatupora atitiqua, Haime, encrusting Gryphcea. 



Lower Lias : about Jamesoni zone. Fenny Compton, Warwickshire. 



X about 28. 

 ,, 3. — D. 7629. Stomatopova antiqv.a, Haime, mut. capricornensis, encrusting 



Montlivaltia Victoria;, Duncan. Middle Lias : zone of L. capricornus, 



Cherrington, Warwickshire, x about 9. 

 ,, 4. — D. 7620, zoarium 4. Another zoarium on the same specimen as Fig. 2. 



x about 8. 

 ,, 5. — D. 7623, zoarium 1. Stomatopora antiqua, Haime, encrusting Gryphcea. 



Lower Lias : about Jamesoni zone, Aston Magna, "Worcestershire. 



X about 11. 

 ,, 6. — D. 7630, zoarium 2. Stomatopora {?) Bichardsotii, sp. nov., encrusting 



Montlivaltia Victoria, Duncan. Middle Lias : zone of L. capricornus, 



Cherriug-ton, Warwickshire, x about 15. 

 ,, 7. — D. 7619, zoarium 1. Stomatopora antiqua, Haime, encrusting Gryphma. 



Lower Lias : about Jamesoni zone, Fenny Compton, Warwickshire. 



X about 8. 

 ,, 8. — <SYowrt/ojyor« i?(V/iffrf?sow?, sp. nov., on a Brachiopod. Lower Lias: about 



Upto)na Jamesoni zone, Toddington, Gloucestershire, x about 15. 

 ,, 9. — Part of the same specimen as Fig. 8. x about 18. 

 ,, 10. — D. 7470, zoarium 1. Stomatopova Gregoryi, n.sp., mut. capricornensis, 



encrusting Montlivaltia Victoria, Duncan. Middle Lias: zone of X. capri- 

 cornus, Cherrington, Warwickshire, x about 12. 



