236 ROBERT TRACY JACKSON ON ECHINI. 



In the Silurian, Echini are represented thus far only in America and England. In t he- 

 Niagara Group of New York State is found the oldest known representative of the Lepidocen- 

 tridae, Koninckocidaris silurica sp. nov. The position of the Niagara is about in the middle 

 of the Silurian. In England, Maccoya phillipsiae (Forbes) is ascribed to the Llandovery which 

 is at the base of the Silurian, but this horizon for the species may be doubted. In the British 

 Museum there is an excellent echinoid lantern from the Wenlock Limestone of Dudley, 1 the 

 oldest assured horizon from which an echinoid is known in Great Britain. In the Lower 

 Ludlow, which is the upper part of the Silurian, just below the Devonian, occur in England 

 Palaeodiscus ferox Salter, and Echinocystites pomum Wyville Thomson, the sole representatives 

 of the order Echinocystoida. 



In the Devonian, as in the Silurian, only a few Echini are known. In the Devonian of 

 Germany Eocidaris laevispina (Sandberger) is fragmentarily known. This is the only species 

 here ascribed to that genus and it is the earliest, also the only known representative of the 

 Archaeocidaridae in the Devonian. In the Devonian of Germany also are found Lepidocentrus 

 rhenanus (Beyrich), L. mulleri Schultze, and L. eifelianus Miiller. Lepidocentrus drydenensis 

 is found in the Upper Devonian of America, in New York State. All species of Lepidocentrus 

 are Devonian excepting one, which is found in the base of the American Lower Carboniferous. 

 In England Lepidesthes devonicans Whidborne and Pholidocidaris acuaria (Whidborne) occur 

 in the Devonian; they are the oldest representatives of their genera and of the family Lepi- 

 desthidae. The imperfectly known Xenocidaris, with three species, is found in the Devonian 

 of Germany. 



The term Subcarboniferous is commonly used in America for the lower part of the Carboni- 

 ferous, below the Coal Measures. I use here the term Lower Carboniferous. This is a more 

 nearly correct name for the horizon and has the advantage of coinciding with foreign usage. 

 The Lower Carboniferous is the period of greatest development of Palaeozoic Echini and it 

 is in America that the most species are found. Here occurs the Miocidaris cannoni sp. nov. which 

 is important as the geologically oldest known member of the Cidaridae, which family is a salient 

 feature of the Echinoid fauna from Mesozoic to Recent times. The genus Archaeocidaris also first 

 appears in the Lower Carboniferous, and in this formation there are many species in both America 

 and Europe. The genus Lepidocidaris, structurally the highest member of the Archaeocidaridae, 



1 Tliis lantern, which was recently discovered in the matrix and developed by Dr. Bather, is well preserved. It has 

 wide-angled pyramids, a moderately deep foramen magnum, and a brace in place. The sides of the pyramids have ridges 

 for the attachment of interpyramidal muscles. It has the essential characters of lanterns, as seen in the Lower Carboni- 

 ferous. As there is no portion of the test in association with the lantern, its generic position is unknown, but it is quite 

 probable that it is a Lepidocentrus or a near ally of that genus. 



1 Dr. Bather called my attention to the fact that Austin (1848) reported that a large species of Echinocrinus [Archaeo- 

 cidaris] occurs in the Wenlock Limestone, Silurian, of Glidden Hill, which is near Coalbrookdale in Shropshire. There is 

 no recognizable description, and the specimen is unknown. If this observation should be confirmed, it would greatly ex- 

 tend the geological range of the genus. 



