78 REPORT — 1875. 



Bridge he had found numerous scattered fish-remains of Rhaetic age, including 

 Saurichthys and Acrodus, mentioned above, foimd also with the Thecodontosmtrm 

 and Palaosaunw on the Mendips ; and he could therefore come to no other conclu- 

 sion than that the deposits were equivalents in time, and that the Durdham Down 

 reptilia must be referred to the Rhsetic age rather than to the Magnesian Limestone. 



On the Bistnbution of Flint in tlie Chalk of Yorkshire. By J. E. Moetimee. 



On Azygograptus, a neiu Genus of Graptolites from the Skiddaw Slates. By 

 H. Alxeyne JSTiCHOLSojr,- M.B., D.Sc, F.R.S.E., Professor of Natural 

 History in the University of St. Andrews. 



In this communication the author recorded a new and remarkable genus of 

 Graptolites from the Skiddaw Slates, founded upon specimens obtained by Mr. W. 

 R. Dover. To this genus the name of Azt/ffoc/rapfiis was given ; and in describing 

 it the author associated Mr. Lapworth with himself, as he was greatly indebted to 

 that gentleman for assistance in working out its true affinities. 



The polypary in Azyr/oyraptus is simple and unilateral, consisting of a single 

 monoprionidiau stipe, which is developed from the central portion of the " sicula " 

 on one side. The cellules are slightly overlapping. 



This genus seems to be intermediate in its characters between the Nemagraptidje 

 and the true Monograptidae, no member of the latter family having as yet been 

 found in strata as old as the Skiddaw Slates. With the Monoyrapti the present 



fenus agrees in the fact that the polj'pary consists of a single unicellular stipe ; 

 ut it diliers altogether from these in its mode of development, the cellidiferous 

 stipe springing directly from one side of the sicula about its centre. In this im- 

 portant character Azyf/oyraptm agrees with no other known Graptolites than JVe- 

 mayraptus, Emmons, and Cmiograptus, Hall, both of these, however, including 

 bilaterally developed forms. The cellules of Azyyograptus .are essentially of the 

 type oi MonoyraptKS Nilssom, Barr., and in this respect the genus is connected in- 

 ditFerently with either the MonogTaptidse or the Nemagraptidaj. 



The only known species of the genus was described under the name of Azyyo- 

 graptus Ldpu'urtlii. It is a slender form, about an inch in length as a rule, and 

 hitherto obtained by Mr. Dover only in the Lower Skiddaw Slates of Hodgson- 

 How Quarry, near Portinscale. It is very readily recognized, even in small frag- 

 ments, by the unique appearance presented by the triangular sicula standing nearly 

 at right angles to the slender celluliferous stipe. The fact also that the stipe 

 originates from the centre of the sicula, below its broader end, gives it a most 

 characteristic appearance, and prevents its being confoimded witli a broken Didy- 

 tnograptus. 



On the Central Group of the Silurian Series of the North of Enyland. By 

 H. AiXETNE Nicholson, M.D., D.Sc., F.R.SE., Professor of Natural History 

 in the University of St. Andrews, and Chaeles Lapwoeth, F.G.S. 



In this communication the authors record the results of their investigation of the 

 central series of Silurian deposits which intervene between the Borroicdale series 

 of volcanic rocks ("Green Slates and Porphyries") on the one hand, a)id tlie Corns- 

 ton Flcif/s on the other. They conclude that the series in question may be naturally 

 grouped as follows, in ascending order : — 



A. The CoNiSTON Limestone series, composed of 



a. The Diifton Shales. 



h. The Cmiiston Limestone, 



c. The Trinucleus Shales. 



B. The CoNiSTON Mudstone seeies, composed of 



u. The SkeJyill Beds, 

 h. The Knock Beds. 



