no. 1646. REVISTON OF BEYRICHIIDjE— ULRICH AND BASSLER. 31 5 



Except the ventral pouch, all the above-mentioned departures from 

 the typical Silurian Beyrichise are toward the new Devonian and Car- 

 boniferous genus HoUina. Indeed, were it not that T. lyoni still 

 possesses the Beyrichian ventral pouch, the writers would undoubt- 

 edly have referred the species to HoUina. But, having a pouch, and 

 being also in other features nearer Beyrichia than is any one of the 

 species of HoUina, the intermediate position of T. lyoni seems as- 

 sured. As its inclusion in either of these genera would introduce 

 undesirable elements of uncertainty in their respective diagnoses, it 

 has been thought advisable to give it and any other similar species 

 that may be discovered an independent position. 



Genus HOLLINA, new. 



CtenobolMna (part) Ulrich, Jour. Cincinnati Roc. Nat. Hist., XIII, 1891, 



p. 1ST: XIX, 1000. p. 182. 

 Beyrichia (part) Jones, Quart. Jour. Geol. Soc. London, XLV1, L890, p. 



538— Ulrich, Jour. Cincinnati Soc. Nat. Hist.. XIII, 1891, p. 189. 

 Bollia (part) Ulrich, Jour. Cincinnati Soc. Nat. Hist.. XIII, 1891, p. '-'it;,. 



Carapace elongate, produced and tapering somewhat anteriorly, 

 essentially equivalved. Valves provided with a marginal frill, con- 

 cave on the inner side, overhanging the contact edge, often wanting 

 at the anterior end. Except for two constant rounded nodes, the 

 lobation of the surface varies greatly. One of the constant nodes is 

 situated close to and partly in front of the middle of the hinge line; 

 the other, usually the smaller, is placed lower and more or less be- 

 hind the center of the valve. Occasionally the hollow between these 

 two nodes is excavated. In most species there is a continuous or 

 broken ridge in the ventral part; in one (77. kolmodini) this ridge 

 continues up the hinder end to the dorsal angle, in others (II. in*<>l< ms 

 and //. tricollina) the post-dorsal extremity remains prominent and 

 forms a rounded node, the remainder of the ridge being dissected 

 and tending to obsolescence; in two other species (II. granifera and 

 II. antespinosa) the ventral ridge joins the two constant nodes, the 

 result, being a loop as in Bollia. Finally, in a later stage (as, f<» 

 instance, //. radiata) the ventral ridge is obsolete and only two 

 rounded nodes remain. Occasionally an extra node is developed near 

 the anterior margin. A ventral pouch, as in Beyrichia, has not been 

 observed. 



Genotype. — HoUina insolens (Ctenol)oll>inn insolens Ulrich). 

 Seven other middle Devonian species and four Carboniferous species 

 are referred here as follows: II. antespinosa, II. armata, II. cavimar- 

 ginata, II. informis, H. spiculosa, all described b}^ Ulrich as specie-; 

 of CtenoboTbina, and H. kolmodini and II. tricollina, originally re- 

 fered to Beyrichia, the first by Jones, the second by Ulrich. The 

 Carboniferous species are II. granifera, a Spergen species described 



