PRODUCTUS. SPIRIFER. TEREBRATULA. 



(fgs. 9, 10), -(Latin, drawn out, dilated) ; or Leptena (from the 

 k leptos, slender). 



Fig. 9. Productus depresses. 



Fig. 1Q. Productus antiquatus. 



"The genus Productus has received its name from a peculiarity observed 

 in several species where the dorsal valve, after having attained a certain 

 magnitude, bends suddenly at right-angles to its former direction, and is 

 then continued irregularly, sometimes being produced (extended) to a con- 

 siderable length. The whole shell is usually covered with striae and spines, 

 which in some species are numerous and very long, and which appear to 

 have been movable, doubtless serving a purpose in the animal economy." 

 Ansted. 



32. The Spi'rifer (Jig. 11), (from the Latin spira, a wreath or 



twisting, and fero, I bear), is a bra- 

 chiopod, closely resembling the tere- 

 bratula in many important characters, 

 but differing from it in the singular 

 spire of calcareous matter passing 

 across the interior of the shell, and 

 from which the name of the genus 

 is derived. The species are very 

 numerous, and, next to terebratula, 

 are the most abundant of all brachiopod fossils. 



33. The genus Terebra'tula (figs. 12, 13, 14), (from the Latin 



terebrOj I bore ; bored, alluding to the perforated 

 beak). Throughout the whole of the pakc'ozoic 



Fig. 11. Spirifer trigonalis. 



Fig. 12. Terebra. 

 tula digona. 



Fig. 13, Tfrebra- 

 tula octoplicata. 



Fig. 14. Terebratula 

 navicula. 



formation, certain species of terebra'tulae are found. This remark- 

 oble genus, which has in the present day some representatives in 

 'he existing seas, appears to have been created among the very first 

 of the inhabitants of the first formed ocean, and to have retained 



32. What is the peculiarity of the Spi'rifer ? 



33. What are terebratula? ? 



