Dr. C. A. Kofoid on Pleodorina illinoisensis. 139 



Skull : basilar length (of a second specimen) 47'5 ; nasals 

 (of type) 18-3 * x 8*5 ; interorbital breadth 20*5 j inter- 

 temporal breadth 19*2 ; diastema 178 ; length of upper molar 

 series 10'4. 



JBab. Mouth of Coca River, Upper Rio Napo. 



Type. Male. B.M. no. 0. 6. 3. 4. Collected in June 1899 

 and presented by Mr. Walter Goodfellovv. 



It is probable that just as S. tricolor ranges northwards 

 from Maynas to the Coca River, so S. cocalis will be found to 

 range up that river westwards and northwards, and that the 

 two species only overlap just at this point. As the two 

 species are found together it may be well to emphasize their 

 differences by repeating that S. cocalis, as represented by 

 seven specimens, differs from S. tricolor (1) by its grizzled 

 instead of blackish crown, (2) by the light patches behind the 

 ears, (3) by its bright orange instead of chestnut fore limbs 

 and hind feet, (4) its black-lined sides, (5) its basally ringed 

 caudal hairs, and (6) its shorter muzzled skull. 



Sciurus pyrrhonotus, Wagn. 



Yungas and Missiones, on the Upper Mamore", Bolivia 

 (Z. Balzan, in Museo Civico, Genoa). 



The type locality of S. pyrrhonotus is Borba, near the mouth 

 of the Madeira, so that its occurrence on the Mamore', on the 

 far upper waters of that stream, affords another instance of 

 the manner in which the ranges of these squirrels follow the 

 lines of the great Amazonian rivers. 



XV. — Plankton Studies. — II. On Pleodorina illinoisensis, a 

 neiv Species from the Plankton of the Illinois River. By 

 C. A. Kofoid, Ph.D.f 



[Plates V. & VI.] 



The genus Pleodorina was discovered in 1893 by Shaw 

 (1894) at Palo Alto, California, and in May of the following 

 year the species Pleodorina cahfornica, upon which the genus 

 was founded, was detected by Mottier (1894) in water from a 

 shallow stagnant pool near Bloomington, Indiana. During 



* Diagonally. 



t From the ' Bulletin of the Illinois State Laboratory of Natural His- 

 tory,' vol. v. pp. 273-293. From a separate impression communicated by 

 the" Author. 



