RETEOCRINID^. 175 



extent by hard matrix ; and we are imable to say at present to what genus 

 they belong. 



S. A. Miller, in his arrangement of the Lower Silurian Camerata in 

 1883,^ united Reteocrinus and Xenocrinus with Archwocrimis, Cupulocrinus, 

 Glyptasier^ Glyptocrimis, and Lampierocrinus in one family, under the '^ Glypto- 

 crinidaB." It is not clear to us upon what this classification was based, since 

 the author did not discriminate between the presence or absence of infra- 

 basals as a family distinction, nor between a regular or irregular arrange- 

 ment of the interradials ; nor did he give attention to the structure of the 

 anal side, upon which most writers, and Miller himself, have relied for 

 excellent family characters. In a later paper on Gli/ptocrinus and allied 

 forms,t he states that the presence or absence of " subradial " plates, the 

 presence or absence of ^^ secondary radials," the structure and form of the 

 cohimn, and the presence or absence of a " proboscis," are the principal 

 characters upon which '' the genera of this special group " have to be separ- 

 ated. All of these rules are in a greater or less degree infringed by Miller 

 himself, l^m '^ Glt/ptocriiius^' parvus has infrabasals ; his '^ GlyptoaHnus Forn- 

 sJielli, a pentangular stem instead of round as in the typical species. A " pro- 

 boscis," such as occurs among the Actinocrinidae, does not exist at all in this 

 group, or at least has not been observed. Neither do we find that the 

 proximal distichals are ever free arm plates, as Miller claims to be the case 

 in '' Pi/cnocrinus!' The specimens which he refers to this genus, and which 

 he kindly sent us for comparison, have from one to two interdistichals, and 

 necessarily had " secondary radials." 



In Miller's classification of 1889, :|: the " Glyptocrinidae " embrace the 

 genera Archceocrimis^ Glyptocrinus^ Cojnpsocrinns, Fycnocrinus, and Schkocrinits , 

 which, as we think, are representatives of almost as many families. He 

 there makes Xenocrinus the type of a distinct family, refers Glyptasier and 

 Lampterocrinus to the GlyptasteridaB, and places Gaurocrinus^ Reteocrinus, 

 Raphanocrimis, and Tliysanocrimis under Gaurocrinidse. 



The Eeteocrinidge are restricted to America, where only seven species 

 have been discovered. 



* Amer. Palseoz. Foss. (ed. 2), p. 276. 



t Dec, 1883 ; Journ. Cincin. Soc. Nat. Hist., pp. 218-219. 



% North Amer. Geol. and Palseoiit., pp. 214 to 215. 



