CACOPS ASPIDEPHORUS - 259 



many of the shields. In the middle of each above there is a shallow- 

 groove bordered on each side by a slight elevation. 



In the structure of the dorsal shield or carapace the genus is identical 

 with Dissorophus, save that the carapace of the latter genus is very much 

 more Qxteilsive, covering practically the whole of the dorsal side of the 

 animal and probably extending further back. Furthermore, in Dissoro- 

 phus the anterior shield is very large, covering several vertebrae, very 

 much like the anterior shield in certain armadillos. That these differ- 

 ences in the carapace, together with others of the skeleton, as shown in 

 an excellent specimen of Dissorophus in the University of Chicago col- 

 lections, which will be fully figured later, are not due to age, is evident 

 from the close correspondence in all skeletal characters between several 

 specimens found associated in the present matrix. These differences will 

 be summarized in the taxonomic discussion on a later page. 



CARAPACE IN ALLIED FORMS 



Most remarkably similar are the dorsal shields of the genus Aspido- 

 saurus Broili, which in other respects, so far as the skeletal characters 

 are known in the rather fragmentary type, resembles so closely the present 

 form that I was for a long time almost assured of their identity, and 

 this opinion was also shared by Doctor Broili, to whom I sent for com- 

 parison photographs of the drawings of the plates illustrating the present 

 paper. But a careful study, not only of the figures and descriptions given 

 by Broili, but also of a fragmentary specimen in our present collections, 

 which must be identified as conspecific with the genotype of Aspidosau- 

 rus, quite convinces me, as it has also Doctor Broili, of the generic dis- 

 tinction between the two forms. 



In Aspidosaurus there is but a single dermal expansion over each spine, 

 apparently coossified or continuous with the top of the spine, which over- 

 laps the preceding one like shingles on a roof. Or, as Broili has stated it : 



"Diese Hautverknockerungen treten nun in innige gegenseitige Verbindungen 

 insofern sich dieselben aufeinanderliegen und zwar immer die folgenden auf 

 die vorausgebende Ossification, wodurcb das Ganze gewisse Aebnlichkeit uiit 

 dem First eines Hauses gewinnt. Diese eigentbiimlicbe Scbutzapparat fallt 

 uocb besonders durcb seine Skulptur auf, welcbe die namlicbe kraftige Ausbil- 

 dung zeigt, knotchenartige durcb Leistcben verbundene Auscbwellungen, wie 

 der Schadel. Die Unterseiten dieser Hautverknockerungen sind glatt, nur 

 ihrer seitlichen Rander weisen leicbte Einkerbungen auf." » 



Of the specimen above mentioned I give figures (plate 10, figures 2, a, 

 h) showing this very characteristic difference. It is seen that the broad 



« Paleontographlca, vol. 11, 1904, p. 42. 



