320 On Diplograpsus pristis loitli Reproductive Capsules. 



here described ; upon the surface of the shale on which thej 

 occur there are numerous young graptolites in various stages 

 of growtli ; and in one specimen figured, " in connexion with 

 one of the sacs there are two miniite germs' one of them lying 

 beneath the sac, and the other just beyond its outer margin 

 and barely separated from its hbres"*. 



Th'e presence of these reproductive capsules throws some 

 light upon the affinities of graptolites. It confirms the evi- 

 dence which their internal structm-e has already furnished, of 

 their near alliance Avith the Hydroida. The reproductive 

 organs of the Actinozoa and of the Polyzoa being internal, 

 graptolites cannot, as some think, belong to either of these 

 classes. In the Hydrozoa tliey are external ; and in some of 

 the Hydi'oida (the only subclass of the Hydrozoa with which 

 graptolites, having a chitinous polypary, can be compared) 

 there are reproductive capsules essentially similar to those of 

 the graptolite, although in no single instance entirely agree- 

 ing with them. We have no single recent Hydroid with 

 reproductive organs enclosed in chitinous capsules which are 

 destitute of any distinct orifice, are bounded by a marginal 

 fibre, or composed of two membranes miited at their edges, 

 and at the same time bud from the periderm without inter- 

 fering with the continuity of the hydrothecffi ; but these ap- 

 pearances are all presented by one or other of the Hydroid 

 zoophytes. In Sertularia, Diphasia^ &c., the gonotheca? bud 

 from the periderm in the same manner as in the graptolite; 

 in several genera they are ribbed or thickened at their edges, 

 and in one genus, if not in more, they have no definite distal 

 orifice. In ArjlaopJienia^ I have been kindly informed by the 

 Rev. Thomas Hincks, the gonotheca " is oval in form, without 

 orifice, and bomided by a very thin and delicate chitinous 

 wall." 



I need only add that graptolites, having, as is here shown, 

 true gonotheca3 as well as hydi'othecas, are most nearly and 

 intimately allied to that order of the Hydroid Coelenterata 

 known as the Thecaphora or Sertularina. 



The specimen which has formed the subject of these remarks 

 was collected by the Geological Survey of Scotland, at Lead- 

 hills, Lanarkshire, along with a series of fossils wliich parallel 

 the rocks of this locality with those of Moftat, Dumfriesshire, 

 or with the Llandeilo Flags of Wales. 



* C4rapt. Qiu^bpc Group, fxpl. ])1. b. fig. 8. 



