Of the subspecies of _T. spinifer_, _asper_ has a proportionately wide head that is closely approached in the subspecies _guadalupensis_ and _emoryi_; _T. s. asper_ differs from _guadalupensis_ and _emoryi_ in having a wider carapace, and resembles _hartwegi_ and _spinifer_, but differs from the other subspecies in having the carapace widest at a plane approximately one-half way back on the carapace. _T. s. asper_ differs from the other subspecies in having the shortest plastron. _Remarks._--Stejneger (1944:72-74) has discussed the history of Baur's _Platypeltis agassizi_. Briefly, Agassiz's description of _Platypeltis ferox_ wherein he (1857:402) states that "The young ferox [Pl. 6, fig. 3] has two or three concentric black lines separating the pale margin ...," was applicable to _T. s. asper_. Agassiz mentioned also that the young of his _Aspidonectes asper_ (_op. cit._:406) "as in Platypeltis ferox, ... has ... two or three black lines separating the pale rim of the posterior margin, ..."; however, _A. asper_ was distinguished chiefly by the "... prominent warts of the bony plates (_loc. cit._)." Because the description of the pattern of _ferox_ resembled that of _asper_, the validity of _asper_ was not agreed upon by all workers. Boulenger (1889:245, footnote 1) referred to _asper_ as a species that required "... further investigation." Baur (1888:1121) realized that Agassiz's description of _ferox_ was not that of _Testudo ferox_ Schneider, and regarded the description of Agassiz as applying to a new species, which he named _Platypeltis agassizii_; Baur (_op. cit._:1122) also recognized _asper_, referring it to the genus _Aspidonectes_. Baur designated a specimen from Georgia (the only individual seen by him) as the type of _agassizi_ (Stejneger, _op. cit._:73, footnote); this specimen is now MCZ 37172. Five years later (1893:218), Baur discussed generic relationships of trionychids, seemingly only on the basis of skulls (holotype of _agassizi_ not mentioned), and referred _agassizi_ to the resurrected genus _Pelodiscus_ Fitzinger, 1835, which was distinguished from the other two American genera that Baur recognized (_Platypeltis_ and _Amyda_) by having the "Posterior nares reduced in size by the inner and posterior extension of the maxillaries." Baur also transferred _asper_ to the genus _Platypeltis_, and restricted the type locality of that species to "Lake Concordia, La." (_op. cit._:220); the type locality of _agassizi_ was restricted to "Western Georgia" (_loc. cit._).