CYCLOPIDIUS 255 



Specific Characters and Discussion: Cope defined the species as smaller than C. simus, with 

 the styles on M 1 much smaller than in that species; in fact, he stated that there are no distinct vertical 

 ribs. M 1 is prismatic rather than quadratic. P 4 is of the same constitution as that of C. simus, 

 according to Cope, but is "relatively much smaller, not equalling in the extent of its grinding face one 

 column of the first true molar." The infraorbital foramen is larger than in some species and located 

 above P 3 . Later Cope (1884B, p. 559) said that P 4 had the same form as in C. decedens (really 

 P 3 ), and he reemphasized the prismatic shape of M 1 and its absence of external ribs. He then 

 stated: "It is quite possible that it [C. heterodon] does not belong to this genus." 



Matthew (1899, p. 73) believed the species to be invalid and said that these teeth were "prob- 

 ably the milk dentition of a smaller species of Cyclopidius." Loomis (1925A, p. 248) considered 

 this form as synonymous with C. simus. I disagree with Matthew in thinking that these are milk 

 teeth. Schlaikjer (1935, pp. 159-161) maintains that it is a valid species and designates Cat. No. 

 2,849 M.C.Z., a skull and jaws, as the neotype. He summarizes the characters as follows: 



One of the smallest known species of Cyclopidius. Mesostyle, especially on M 1 , very weakly developed. 

 Molars very much laterally compressed and M 1 shortened. Premolars and molars greatly hypsodont. Incisors 

 \. Lower incisors minute. Skull narrow for Cyclofidius. Facial area narrow and rather elongate. Orbits 

 excessively large. Malar portion of zygomatic arch not developed inferiorly. Antorbital fossre elongated, narrow 

 and almost separated. 



The teeth are much worn in the type, but it was certainly a small animal, with its P 4 and M 1 

 longer than wide. In fact, the lateral compression of M 1 is more pronounced that in any of the other 

 species, which may indicate that we have here a female of C. simus. This is what I shall consider 

 it to be until further material gives more evidence of validity of characters. 



In general, the development of the parastyle and mesostyle on M 1 in Cyclopidius is not 

 pronounced, so that the lack of it on that of C. heterodon is not surprising, considering the size of 

 the animal and that it may well be a female. Schlaikjer is of the opinion that C. californicus is 

 ancestral to C. heterodon. My suggestion is that the former is an aberrant branch of the genus, 

 more advanced in the shortening of the face, and yet older geologically than these Montana forms. 



Measurements in millimeters 

 P 4 , anteroposterior 5; transverse 4.5. 

 M 1 , anteroposterior 8; transverse 6. 



Cyclopidius incisivus Scott 1893 = ? C. simus Cope 



PI. XXXVIII, figs. 6-8 



Original Reference: The mammals of the Deep River beds. Amer. Nat., XXVII, pp. 659, 661-662. 

 Type Locality: Smith River Valley, Montana. 

 Geologic Horizon: Upper Miocene (Deep River). 



Type: Holotype, Cat. No. 10473 P.U.M., anterior part of skull with teeth. Collected by R. A. Stevenson, 

 1891. 



Specific Characters: Scott (1893) described the species thus: "Like C. simus, but having 

 two small incisors in each premaxillary ; the latter bones also of a different shape from those of the 

 former." 



With more abundant material, since discovered, we are aware that both of the above distinctions 

 are no longer valid. The teeth are quite similar between this species and C. simus, the index of M 1 

 in the former being 1.11 and in the latter 1.12. The molar and premolar tooth rows are a little 

 longer in C. incisivus, but the proportions are quite similar, the index for that species being 0.78 and 

 for C. simus 0.75. 



The peculiar twist of the premaxillary bones through 90° as they ascend from the alveolar 

 border is a generic characteristic. A beginning in this direction is seen in Leptauchenia. 



For the present I consider this species as a variant of C. simus, and I am in agreement with 

 Loomis and Schlaikjer on this point of synonymy. 



