H 7 att.] 294 [April 4, 



species have fluted, and often hollow abdomens. The siphon is 

 above the centre in all except radical forms. The sutures ac- 

 quire ventral, lateral, and dorsal lobes, and annular lobes in the 

 higher nautilian species of Vestinautilus. The radical of this 

 family is Thoracoceras among the Orthoceratidae, and this genus 

 could be very appropriately included in this family. The type 

 is the Thor. Vestitum Eichw. Bull. Soc. Imp. de Mosc. 1844, 

 p. 761, pi. 17. It includes Thor. (Cyrt.) corbulnm, sp. Barr. pi. 

 125 of the Silurian, and several Devonian species, besides the 

 Carboniferous spinous ridged species like Thor. (Cyrt.) canalicu- 

 latum, sp. DeKon. Calc. Carb. pi. 33, and also the frequently 

 smooth ridged arcuate forms, like Thor. (Cyrt.) Puzosianum, sp. 

 DeKoninck, which have similar transverse striae though less 

 prominent. The connection between this genus, and Triboloceras 

 is too close to need discussion. A connection with the Trigon- 

 oceratidae can also be inferred from the resemblance of the adults 

 of such species as Thor. Puzosianum, and the young of some 

 forms of Trematoceras and Discitoceras. But the connection 

 with Trigonoceras is made very doubtful by the transverse costae 

 of that genus, the form, and the modifications of the dorsal 

 sutures. We incline, therefore, to separate the group at least 

 provisionally from the Trigonoceratidae. 



Triboloceras, 1 nobis, includes the remarkable series of gyro- 

 ceran, Carboniferous species described by De Koninck in his 

 Calc. Carb., which have subspinous ridges in the young until a 

 late stage of growth, and otherwise resemble the adults of Thor- 

 acoceras. The whorl in section is more or less depressed, and 

 either biangular with convex abdomen and gibbous dorsum, or 

 approximately triangular with concave abdomen. The siphon 

 is above the centre. The sutures have broad, ventral, and 

 lateral lobes, and dorsal saddles without annular lobes. Type, 

 Tribo. (Gyr.) serratum, sp. DeKonnick, Calc. Carb. pi. 32, fig. 5. 

 Mus. Comp. Zool. The forms range from Tribo. (Gyr.) pro- 

 pinquum, ibid., pi. 33, to Tribo. (Naut.) Meyerianum, ibid., pi. 29. 

 Vestinautilus, Ryckholt, includes nautilian species of the 

 Carboniferous with depressed subtri angular, or trapezoidal whorls, 

 the abdomens very broad, and the dorsum with an impressed 



i TptPoXos, a burr. 



