458 MR. S. S. BUCKMAN ON THE BAJOCIAN [Aug. 1 895, 



the term ' heterochronous homceomorphy ' to the phenomenon * ; 

 and the term ' isochronous homceomorphy ' would describe the re- 

 semblance between the contemporaneous Buckmani with its deriva- 

 tives, and cortonensis with its developments. These are species 

 geographically isolated : but isochronous homceomorphy would be 

 applicable to the likeness between heterogenetic species of similar 

 geographical range — for instance, T. Stephani and T. Phillipsi. 

 Again, in the case of the Cotteswold forms, T. plicata and T. fimbria, 

 both heterochronous and isochronous homceomorphy are in evidence. 

 Thus these two species are not descended one from the other ; but 

 they are heterogenetic multiplicate derivatives from a non-plicate 

 circular form. Elongation and subsequent acquirement of folds 

 produces T. plicata, a common fossil of the Pea-grit (Murchisono? 

 hemera), where the circular form also acquires plications (T. fimbria), 

 but is rarely met with. Later, in the Oolite Marl (bradfordensis 

 hemera), the circular plicate form (T. fimbria) is common; and it 

 shows a tendency to elongation with excessive plication at a still 

 later date (Upper Freestone) ; while, somewhat before T. fimbria 

 became common, the elongate, plicate form (T. plicata) dies out, in 

 the early part of the Oolite Marl, where are found a few modified 

 (aged) descendants of the true plicata of the Pea-grit. 



These remarks will show the kind of revision which the Jurassic 

 brachiopoda require, in order that their genetic affinities may be 

 understood, and also that specific names may be properly applied so 

 as to enable such genetic affinities to be expressed. They also indi- 

 cate the reason for the present application of certain new specific 

 names. 



2. The Oolite Marl Series and its Brachiopod-sequence. 



This includes the ' Oolite Marl ' and the ' Upper Freestone.' It 

 is obvious to those who work in the Cotteswolds that these terms are 

 purely arbitrary ; because marly conditions prevailed at one locality 

 contemporaneously with freestone conditions at another. A good 

 exposure of the series may show very little freestone at all, but 

 much marl ; and it may be all the more welcome to the geologist. 

 Such is the exposure at the Frith (p. 399) : this is one of the finest 

 and most prolific in the Cotteswolds ; its rival is that shown in the 

 railway-cutting at Notgrove Station, distant 16| miles N.E. by E. 

 The upper beds of the series are more prolific at the Frith, and 

 the lower beds at Notgrove Station. I gave a section of the latter 

 locality in Proc. Cotteswold Nat. Field-Club, vol. ix. pt. ii. (1887) 

 p. 114 2 ; and the Frith section may be advantageously compared 

 therewith. It will be seen that at the Frith there is 19 feet 9 inches 

 of strata in the Oolite Marl series above the Rh. subobsoleta-h.ori7.on, 



1 It might arise from divergence ; and this term proposed does not commit 

 us to the means whereby the result is obtained, it only describes the effect 

 produced. 



2 Of Bed 21 of that section 9 lbs. yielded 563 specimens, excluding micro- 

 morphs ; they were mostly brachiopoda. Many were crushed. 



