360 TEREBRATULID^. 



other Mediterranean species, are better known examples. 

 Several species are known fossil, ranging as far back as the 

 Cretaceous epoch. They differ so materially from the 

 Terebratida, properly so called, that Dr. Philippi has been 

 induced to consider them as members of the fossil genus 

 Orthis, with which, however, they have no near affinity. 

 M. Alcide d'Orbigny has associated Megathyris with 

 Thecidea, forming of these genera his Thccidida, the second 

 family of his second order, AbracMopoda of Palliobranchi- 

 ata* But, though fully prepared to admit the just claims 

 of these brachiopods to generic distinction, we can scarcely, 

 in the present state of our knowledge, regard them as 

 farther removed from Terebratida proper than Lingida, 

 Productus, or Crania, as M. d'Orbigny would place them; 

 whilst he associates them in the same great group with the 

 anomalous Budistce, which appear really to have much closer 

 relations with Crania. Although Philippi describes Tere- 

 bratula detruncata as having no arms, but only cirrhi 

 attached to the apophyses, our own examination of that 

 animal would rather go to maintain the existence of true 

 but fixed arms ; and in the curious Orthis anomioides of 

 Scacchi and Philippi (which is the Terebratida depressa 

 of the "Report on the Mollusca of the TEgean" ), the 

 latter eminent malacologist figures and describes two perfect 

 spiral cirrhigerous arms, the species in question evidently 

 having no very distant affinity with that Avhich we are 

 about to describe. 



The few living species known of this interesting genus 

 are inhabitants of deep — often very deep — water, where 

 they are found adhering to stones and corals. It is most 

 jikely that, generally speaking, the Orthidiform brachio- 

 pods indicate a considerable depth of water, and that their 



* D'Orbigny, "Terrains Cretaces," vol. iv. p. 7. 



