GEOLOGY. 323 



the occipital and parietal ridges, the strength of the zjgomatic arches, and the 

 expanse of the temporal fossre all indicating the possession of temporal (biting) 

 muscles as largely developed as in the most powerful and ferocious of the car- 

 nivorous mammalia. This unique modification of a sauroid skull is associated 

 with the presence of a pair of long, curved, sharp-pointed, canine tusks, descend- 

 ing as in the machairodus and walrus, outside the lower jaw when the mouth is 

 shut, these tusks being developed to the same degree as in the smaller species of 

 Dicynodon (D. lacerticeps, D. testudiceps, etc.), described by the author in a former 

 memoir ; and, as in those species, so in the present more gigantic one, no other 

 trace of teeth was discernible, the lower jaw being edentulous, as in the extinct 

 Rhynchosaurus, and the Chelonian reptiles. Most of the extinct reptiles ex- 

 emplify the law of the prevalence of a more general structure, as compared with 

 the more specialized structures of existing species. The Labyrinthodonts com- 

 bined sauroid with Batrachian characters; Rhynchosaurus, saurid with Chelo- 

 nian characters. The Ichthyosaurus had modifications borrowed from the class 

 of fishes, and the Pterodactyle others borrowed from the type of birds and bats 

 in both cases engrafted on an essentially sauroid basis. The Dicynodonts 

 which were like lizards in their more important cranial character, as for ex- 

 ample, the divided nostrils, the dependent tympanic bone, and the pair of 

 symmetrical suboccipital processes resembled the crocodiles hi the extent of 

 ossification of the occiput, resembled the Tryonyces in the extent of ossi- 

 fication of the palate, and in the form and position of the posterior nostril ; 

 and resembled the Chelonia generally in the edentulous trenchant border of 

 the whole of the alveolar part of the lovrer jaw, and of a great part of that 

 of the upper jaw. But they also superadded to this composite reptilian 

 structure of the skull a pair of long, sharp, descending tusks, and temporal 

 fossae and ridges, which seem to have been borrowed from the mammalia- 

 class. 



NEW 3IIXERAL OOGUAXOLITE. 



At a recent meeting of the Boston Society of Natural History, Dr. A. A. 

 Hayes presented a specimen of a fossilized egg from the Guano Islands, off 

 the coast of Peru, which in its interior contained a new mineral compound. 



The form of the original mass was ovoid, the circular outline having been 

 reduced by compression, about one third. Externally rough, from adhesions, 

 there were smooth parts, from which a thin layer could be removed, which 

 when cleaned, had the organized structure of egg shell, although partly 

 changed in chemical composition. In the examination of one half of the 

 specimen, fragments of shell were found, crushed into the mineral occupying 

 the cavity. The color of the mass was Xankin-yellow externally, deep yel- 

 low and reddish brown within. The compact parts scratched calcareous spar, 

 its general hardness fully equaling that of this mineral. The fracture of the 

 mass exhibited a crystalline structure, most remarkable near the center, where 

 the yolk may have decomposed. The crystals, in no case distinct, presented 

 an aggregate of flat, plumose prisms, radiating from centers ; these have a 

 marked pearly, or satin-like luster, and readily divide along natural joints. 



