THE TANGANYIKA PROBLEM. 



259 



the median tooth are the different species of the genus 

 Sigaretus. 



In Spekia zonata the oesophagus leads into a double 

 stomach, of which the anterior chamber contains a crystal- 

 line style ; but it is so small and so little elongated that at 

 first sight it does not seem to have the characters which 

 this structure usually presents. 



The intestine takes the course represented in figure 

 42, and communicates with a dilated rectum, opening 

 in the usual way just within the border of the mantle. 



Fig. 42. — Semi diagram of the anatomy of Spekia zonata. 



The heart has the regular tsenioglossate characters. In 

 S. zonata, owing to the naticoid shape of the body, there 

 is a forward displacement of the internal viscera, which 

 results in the pulmonary vein not going directly forward to 

 the base of the stenidium, as in Tanganyicia rufofilosa and 

 most other Prosobranchs, but in its being bent slightly 

 backwards in a more or less acute curve before it reaches 

 the base of the gill. This relative displacement of the 

 heart and gill is fully described by Haller in the Naticas 

 Trochita radians, Ergcea plana, Crepidula peruviana 

 (Lam.), Tanacus ungidformis (Lam.), and Crucibulum 

 (sp. ?), and it is curious to find that this displacement has 



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