1846.] MORRIS ON TEREBRATULA. 383 



being continuous throughout, but separated into two distinct parts; 

 and although all the species so arranged by Von Buch do not ex- 

 actly accord with the sections we now propose, it is interesting to 

 observe that nearly all of those belonging to the first section are also 

 species of our second group Hypothyridce, and are not punctate, 

 while the second and third sections contain, with very few excep- 

 tions, all the species included under our Ejnthyridce, or punctated 

 group. In speaking merely of the Terebratulae, it is not necessary 

 to refer to the other subdivisions of the Brachiopoda proposed by 

 Sowerby, Dalman, Von Buch, or Professor Phillips; the latter adopts 

 the variation of the foramen as the principle of his classification, 

 and subdivides the genus Terebratula (^Cyclothyridce) into Epithy- 

 ris and Hypothyris, as indicating the position of the foramen, these 

 two groups nearly according with the view adopted in the present 

 memoir. 



In my early investigations of the Terebratulae, I ascertained that 

 among the recent species, one only, T. psittacea, was not punc- 

 tated*, and this species also has an acute beak, below which there is 

 a deltidial opening, the deltidium being scarcely developed on each 

 side, and a slight apophysary system. Of this type there is now 

 another recent species known, whilst all the other recent species 

 with which we are acquainted have a minutely punctated struc- 

 ture, the beak of the dorsal valve being more or less truncate, and 

 the internal apophysary system more developed. 



Dr. Carpenter has also added considerably to our knowledge of 

 the structure of Terebratula, in his Report to the British Associa- 

 tion *0n the Microscopic Structure of Shells,' and after examining 

 about fifty species, he arrives at the conclusion, "that with scarcely 

 an exception, the perforated (punctated) species are smooth, or 

 but slightly plicated, whilst the non-perforated (non-punctated) 

 species are deeply plicated" (Report, 1844, p. 18 f). In this me- 

 moir Dr. Carpenter simply divides the species into perforated and 

 non-perforated, without pointing out any other modification con- 

 nected therewith; but as certain and constant characters, more 

 especially about the foramen and cardinal area, co-exist with the 

 absence or presence of these punctations, 1 think there can be no 

 doubt, as stated in that paper, " that the punctation must have some 

 intimate relation with the structure and habits of the animal, and 

 that it must consequently be a character of zoological importance." 



On separating the two general forms which exist among the 

 Terebratulae, those of plicated and smooth species, it will be found 

 that the majority of smooth species have a truncated beak and a 

 punctated shell ; on the other hand, a very large number of the 



* This fact was mentioned to Mr. J. Sowerby in 1841, and alluded to in his 

 observations on the genus Atrypa, published in No. 108 of the ' Mineral Concho- 

 logy.' 



t In this paper Dr. Carpenter cites T. coarctata and T. fnibrotunda as non* 

 punctated species, and T. acuta as punctated, whereas tlic two former are punc- 

 tated and the latter non-punctated, and therefore agree with the other characters 

 belonging to the foramen, *c. 



2c'2 



