Vol. XIV. February, 1908. No. 3 



BIOLOGICAL BULLETIN 



THE ANNULUS OF A MEXICAN CRAYFISH. 



E. A. ANDREWS. 



It is well known that the females of the common American 

 crayfishes of the genus Cambarus possess a peculiar structure 

 called in systematic descriptions the " annnlus ventralis." In 

 our common northern crayfishes it has been shown (1) that the 

 annulus contains an essential accessory reproductive organ, the 

 seminal receptacle, without which the species would become 

 extinct. Ortmann has recently divided the genus into six sub- 

 genera (2) and also (3 and 4) given reasons for supposing that the 

 seventy or more species of Cambarus now living in the United 

 States and adjacent territory are descended from forms once 

 living in the region now called Mexico. As some of the more 

 primitive subgenera are found only in Mexico and as it is not 

 known whether the annulus in any Mexican crayfish contains a 

 reproductive organ or not it seems worth while to describe the 

 real character of the annulus in any Mexican crayfish that can 

 be obtained. 



The question as to the evolution and spread of the genus 

 Cambarus cannot be completely answered till it is shown that 

 the annulus in all members of the genus does contain the sperm 

 receptacle, and that they thus differ from all other crayfish the 

 world over. 



The crayfishes whose annulus is here described were bought 

 in the market of the city of Mexico, in July l and prove to be 

 Cambarus montezuvuz Saus. of the typical form. 



This species was first described in 1857 by Saussure (5), but 



1 These specimens were obtained by Horace Andrews, C.E. , with the aid of 

 W. W. Blake. They were on sale, cooked, as taken in Lake Zumpango and known 

 by the Astec name " Acociles." 



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