Agassiz (loc. cit.) mentioned that nuchalis "differs strikingly from Asp. spinifer in the much more elongated form of the male, and in the great development of the marginal spines and of the tubercles upon the carapace, … But the most prominent specific character consists in the marked depressions on either side of the blunt median keel, and also in the triangular dilation of that keel behind the front margin of the carapace." These characters seem to be of no taxonomic worth. I have seen three syntypes (MCZ 1623-25) that undoubtedly correspond to the three adult specimens mentioned by Agassiz. All are females, measuring 19.5, 22.0, and 19.0 centimeters, respectively, in plastral length, and lack a contrasting mottled pattern on the carapace; the juvenal pattern is obscured, except for blackish spots at the edge of the carapace on MCZ 1625, and parts of an ocellus on MCZ 1624. The dorsal surfaces of the limbs are boldly marked. MCZ 1623, showing the diagnostic feature mentioned by Agassiz, is photographed by Stejneger (op. cit.:Pls. 14, 15), and may be regarded as the lectotype of Aspidonectes nuchalis Agassiz. MCZ 1908 is one of the young syntypes mentioned by Agassiz, and is referable to spinifer. The juvenal pattern consists of spots and ocelli; the plastron measures 3.1 centimeters in length, and the carapace 4.2 centimeters.
Wied-Neuwied (1865:55-57, Pl. 5) described the species ?G[ymnopus] olivaceus, but was uncertain whether his interpretation was based on a species, a variety or a secondary sexual difference. Wied-Neuwied mentioned that Lesueur had already named this soft-shelled turtle as Trionyx ocellatus, and agreed with Lesueur that those turtles having occulated spots on the carapace were distinguishable from T. spiniferus and T. muticus. But because Duméril and Bibron in their Erpétologie Général failed to recognize T. ocellatus, Wied-Neuwied felt obliged to bring it to the attention of his American colleagues and he renamed it. Wied-Neuwied also stated, in the context of a synonym, "Beschreibung einer Reise in Nord-America Bd. I., pag. 140." This comment presumably refers to his earlier description of T. annulifer (1838:140); seemingly Wied-Neuwied considered T. annulifer and G. olivacea as conspecific, although there is no mention of annulifer in the text proper. Stejneger (op. cit.:49) designated the type locality of T. annulifer as the Ohio River at Pittsburgh, Pennsylvania, and of Gymnopus olivacea as New Harmony, Wabash River, Illinois (lapsus for Indiana).
Trionyx spiniferus was questionably considered distinct from T. ferox by [493] Lesueur who listed "Testudo ferox Gm. Tortue de Pennant?" and "Trionyx georgicus Geoffr.?" as synonyms. Subsequently, most authors considered T. spiniferus synonymous with T. ferox until Agassiz (1857) pointed out differences between the two species.
The average size of the ocelli on the carapace of the subspecies spinifer decreases westward toward the Mississippi River; ocelli of different sizes occur on different individuals from the same state and presumably from the same population. For example, INHS 2281, plastron 9.9 centimeters in length, from Effingham County, Illinois, has some ocelli eight millimeters in diameter, whereas a larger male from the same locality, UI 1322, plastron 11.6 centimeters in length, has the largest ocelli only five millimeters in diameter. For convenience, all softshells having locality data from states east of the Mississippi River are referred to spinifer, recognizing that intergradation occurs with hartwegi over a broad area paralleling the Mississippi River. The type locality of spinifer is in an area where most turtles do not have the larger ocelli (diameter of seven to ten mm. on adult males); however, some individuals from the Wabash River (UMMZ 63523, adult male, plastron 11.5 cm. in length, ocelli diameter seven mm.) agree with more "typical" spinifer to the east. Intergradation with asper possibly occurs in that part of the Tennessee River in eastern Tennessee as exemplified by UMMZ 59198.
Published reports indicate that T. s. spinifer is not abundant in some of the northeasterly parts of its geographic range. Adams and Clark (1958:10) wrote that few softshells at Long Point on the Canadian side of Lake Erie are "ever collected and the area's game keepers report … (none) … seen in recent years. They also tell of recurrent severe stormy winters in which the muddy bottom of the marshland was repeatedly churned up and frozen. Such climatic conditions could easily destroy a large part of the Trionyx population overwintering in the mud bottom." Wright (1919:8) reported that softshells are "rarely seen" in bays on the New York side of Lake Ontario, and Babcock (1938:53) wrote that spinifer "is not common in Lake Champlain."
T. s. spinifer probably extended its geographic range into the Hudson River drainage of New York via the Erie Canal (connected Buffalo and Albany) after its completion in the early 1800's (DeKay, 1842:7). Now, the New York Barge Canal (essentially the Erie Canal, but with minor changes in course and the addition of several spurs) provides an avenue for dispersal of spinifer to the Hudson River drainage, Lake Ontario and intervening waterways in New York (Mertens, 1928:199). Netting (1944:86-87), however, suggested that spinifer occupied Lake Champlain, the Finger Lakes, Mohawk River and upper Hudson in the late stages of the formation of the Great Lakes.
A publication not seen by me is that of Mansueti and Wallace (1960). Its title suggests that Trionyx occurs in Maryland.
The unsuccessful introduction of T. s. spinifer in the Delaware drainage in New Jersey has been discussed by Fowler (1907:213), who wrote that they were found as early as the late 1860's and were introduced when young presumably to stock aquaria. Records of occurrence include Cooper's Creek, Camden County (Stone, 1906:168); Woodbury, Gloucester County (Cope, 1894:889); and Paulins Kill at Hainesburg, Warren County (Johnson, 1894:889).
Surface (1908:122) believed that soft-shelled turtles "have doubtless been [494] introduced into the eastern part of Pennsylvania through the canal from the Western and Central part of New York," and Roddy (in Neill, 1951:21) suggested that the species may be found in the Susquehanna River. Babcock (1919:420) mentioned a young specimen of spinifer in the collection of the Boston Society of Natural History that was obtained "in White River, Vermont," a tributary of the Connecticut River of the Atlantic Coast drainage; seemingly this record has not been accepted and the species is not established. To my knowledge, populations of T. s. spinifer do not occur in rivers of the Atlantic Coast drainage, except probably the Hudson-Mohawk drainage.
Stockwell (1878:401) wrote that spinifer was found "as high as Athabasca." Presumably Stockwell referred to Lake Athabaska in northern Alberta and Saskatchewan, Canada, a region where soft-shelled turtles are unknown; see also the comments by Stejneger (1944:52).