188 Mr. C. Lapworth on the Geological 



Of the genus Climacograptus, Hall, perhaps Climacograptus 

 bicorais, Hall, is the most widely distributed. It agrees pre- 

 cisely in its vertical range with Diplograptusfoliaceus, Murch. 



The conventional genus G. scalaris, His., sp., unites by its 

 so-called varieties the Ordovician and Silurian systems. They 

 make their appearance in the Middle Bala, and die out in the 

 higher Llandovery. 



Cvyptograptus. — The genus Cryptograptus, Lapw., is un- 

 known above the Bala Limestone. Forms allied to Crypto- 

 graptus tricornis, Carruthers, are abundant in the Glenkiln 

 zones. 



Family vii. Lasiograptidse (or G-lossograpticUe). 



We now enter upon very unsafe palasontological ground. 

 The family of the Lasiograptidse is merely an assemblage of 

 diprionidian genera, certainly more closely allied among them- 

 selves than they are, on the one hand, to the typical Diplo- 

 graptida3, and, on the other, to the forms at present grouped 

 in the Retiolitidas. They agree with the former in their 

 general external features and in the continuity of the epiderm, 

 while they differ from them in certain details of internal 

 structure, and in the form and position of the reproductive 

 processes. In these latter respects they agree with typical 

 Ketiolitida?. 



Retiograptus, Hall. — The oldest genus referable to this 

 family is the peculiar form Retiograptus of Hall, which ap- 

 pears to combine in its polypary the marginal meshwork of 

 Lasiograptus and the lateral spurs of Glossograptus. Only 

 two forms are known, and both are of Arenig age. One, R. 

 tentaculatus, Hall, occurs in the Quebec group ; the other 

 has been figured by Mr. E. Etheridge, Jun., from the corre- 

 sponding beds in Australia. 



Glossograptus, Emmons. — This genus ranges from the base 

 of the Arenig to the horizon of the Bala Limestone. Its 

 peculiar forms are very abundant on certain horizons in the 

 Llandeilo of Sweden. In Britain it is usually a rare fossil. 



Lasiograptus, Lapw. — This genus (which includes only 

 those forms in which the reproductive sacs appear to have 

 been protected by a continuous series of marginal meshes) 

 bas not hitherto been quoted from Arenig rocks. It is abun- 

 dant in the Upper Bala, above which it is unknown. 



Hallograptus, Can. — The title of Hallograptus was sug- 

 gested by Mr. W. Carruthers for forms like Biplograptus ? 

 bimucronatus, Hall, in which the gonosome is provided with 

 scopulate reproductive processes. The genus as thus defined is 

 strictly Llandeilo-Bala in range on both sides of the Atlantic. 



