CLASSIFICATION OF THE SCIUEIDyE. 229 



slightly compressed a,nd striolate laterally. Its upper portion is 

 lightly convex, smooth, and cartilaginous, but not ossified. Its 

 lower portion consists of softer tissue, and carries the urethral 

 orifice on a small fleshy process at the distal extremity of its right 

 side. The distal extremity of the glans is long, slender, flexible, 

 and filiform, like a rat's tail. I can find no trace of baculum in 

 it, unless the remnant of this bone is represented by a slight 

 opacity at the distal end of the thread. (Text-fig. 23, A, B.) 



In an immature male of Helioscmrus 'pimictatus the penis 

 resembles in a general way that of H. rufobrachium, being 

 exceedingly long and distally slender and filiform without trace 

 of baculum. The specimen is not well preserved, but the filiform 

 portion appears to terminate in a small arrow-headed tip and to 

 pass into the main body of the penis without the intervention of 

 the swollen glandular portion carrying the orifice such as is seen 

 in H. rufohrachhmi. The position of the orifice I could not 

 determine. 



The differences above described are very considei-able, and if 

 they are found to obtain in adult examples of H. jnmctatus, they 

 ■would, I suppose, indicate a generic difTerence between that 

 species and If. riifohrachmm. But since the example in question 

 is immature and poorly preserved, the examination of fresh 

 material must be awaited ere a decision on the point is reached. 



Temporarily setting aside the penis of the example of Helio- 

 scmrus punctatus above described, the characters of this organ as 

 shown in the other genera may be tabulated as follows : — 



a. Penis exceedingly long, the distal portion of the glans forming 



a long, flexible thread-like termination without baculum Heliosciurtis. 



a' Penis quite short ; the distal portion of the glans shorter, stouter, 

 rod-like, not filiform, and provided with a baculum. 

 b. The narrow rod-like distal portion flexible, with a finelj' serru- 

 lated crest on each side, and carrying a minute baculum near 



its distal end ^tlioscmrus, Funisckmis, Paraxerus. 



h' The narrowed distal portion not flexible, without serrulated 



crests, but supported throughout by a relatively large baculum. Frotoxerus. 



It must be remembered, however, that the characters assigned 

 to the penis of Frotoxerus and jEthosciuriis are ta.ken from 

 Tullberg's descriptions and not from my own observations. 



Despite the differences between the penes of these genera, 

 there are certain significant features they have in common. The 

 glans is divisible into two parts, a swollen proximal portion 

 carrying the urethral orifice and a more slender terminal portion. 



The most primitive type appears to be that of Frotoxerus, 

 where the terminal portion is relatively stout, moderately long, 

 less sharply distinguished from the swollen proximal portion, 

 without serrulated crests, and supported by a well- developed 

 baculum, the proximal thickened end of which is probably lodged 

 in the thickening of the glans, while the apex extends to the 

 arrow-headed tip of the thinnel- distal portion. 



In the next stage, exemplified by ^Ethosciurus, Faraccerus, and 

 Proc. Zool. Soc— 1923, No. XYI. 16 



