Prof. T. R. Jones 8f H. Woodward — Palceozoic Phyllopoda. 539 



Tremadoo rocks) with many - branchecl forms like Clonograptus 

 possessing a symmetrical arrangement : the fewer the branches, 

 however, the greater the supply of food to the entire organism ; 

 consequently we find forms with more than eight branches (^Logano- 

 graptus) rapidly replaced by eight-branched forms (Dichograptus), 

 these by four-branched forms (Tetragraptus), and these, again, by 

 two -branched forms (Bidymograptus). Professor Lapworth has 

 privately furnished us with what is doubtless the reason why 

 unilateral forms like Azygograptus did not survive, until the genus 

 Monograptus became established in the Silurian rocks, but we await 

 the publication of this reason. Four-branched forms descended from 

 one series would be at a disadvantage as compared with two- 

 branched forms of another ; therefore, when once a two-branched 

 form of one series was established, any departure from a four-branched 

 to a two-branched form in another series would tend to survive, and 

 the four-branched forms would die out, hence the general isochronism 

 of forms belonging to diverse series possessing the same number of 

 branches. 



Again, forms having the series of hydrothecas facing one another 

 would receive a smaller supply of food than those having the 

 hydrothecEe further apart ; consequently the increase in the angle of 

 divergence followed, which attained its maximum of 360° when the 

 backs of the stipes came into contact with Phyllograptus, Diplo- 

 graptus, and Climacogi-apttis. 



Lastly, hydrothecee the openings of which faced downwards and 

 lay in the same plane would be jjlaced at a disadvantage compared 

 with those which faced in different directions, hence the variations 

 in the nature of the hydrothec£e resulting in the curved and sometimes 

 twisted forms met with amongst the later Griaptolites. This would 

 also produce its effect upon the angle of divergence. 



The above notes are offered as suggestions only, though in our 

 opinion they are plausible. Should they be correct, the value of 

 Graptolites, enormous as it already is to the stratigraphical geologist, 

 will become equally so to the biologist; and we may look forward 

 to the establishment of a complete phylogeny in the case of this 

 remarkable sub-class. 



II. — On some Paleozoic Phyllopoda. 



By Professor T. Rupeet Jones, F.E.S., and Dr. Henry "Woodwaud, F.E.S. 



(PLATE XV.) 

 1. Ceratiocaris reticosa, sp. nov. Plate XV, Figs, la, lb. 



IN the Museum of Practical Geology there is a specimen of 

 Ceratiocaris (No. 4435), from the vicinit}' of Ludlow, which 

 was not noticed by us in the "Monograph of British Palasozoic 

 Phyllocarida " (Palaeontographical Society), 1888. It is a squeezed 

 carapace, evidently allied to the Ceratiocaris cassioides there de- 

 scribed and figured, pages 59-61, pi. iii, fig. 9; pi. iv, fig. 7; and 

 pi. vii, figs. 4-6. The specimen appears to have been bivalved. 



