44 OUR COMMON BRITISH FOSSILS. 



and are among the prettiest of all the Graptolites. 



Their resemblance to the brass-toothed wheels of 

 watches is often still further borne out by 

 the Rastrites having had their substance 

 converted into iron pyrites, the gilt out- 

 lines standing forth in very bright relief 

 from the surfaces of the black shales in 

 ^ , , which they are imbedded. 



Fig. 32. — Calycles •' 



^^ ^Murchfsold''^ These toothed-projections, seen on the 

 (magnified). ^^^^^ margins of both single and double 

 Graptolites alike, are regarded by most naturalists as 

 identical with the cups of recent " sea-firs," or Sertu- 

 larians, and therefore as having contained zoophytes 

 when the Graptolites were alive. Professor Allman, 

 however, doubts whether the Graptolites had cups at all, 

 and thinks that these projections were like those seen on 

 the embryonic stem of the Lobster's horn Coralline {Aii- 

 tennularia), which bear nematophores. Dr. Nicholson 

 figures the egg-bearing capsules of Graptolites in his 

 ''Manual of Palaeontology," and his " Monograph of 

 the Graptolitidce" where he sets forth their resemblance 

 to the gonotheccB of the Sertularians. He states he 

 found them both attached to the branches of the 

 Graptolites, and separate, and has no doubt as to their 

 being the egg-bearing cases of the ancient Graptolites. 

 Neither Allman nor Carruthers, however, assents to 

 this conclusion. The former believes that the Grapto- 

 lites did not bear egg-cases at all, but developed them- 

 selves by budding, just as the banks of that oceanic 



