702 THE ANIMAL KINGDOM. 



well marked off. The dorsal aspect of the middle segment is large. There is, at 

 least in early stages, no ventral mantle-lobe, and consequently no provisional setae 1 . 

 In Terebratula minor the mantle-folds appear before the terminal segment, and 

 there is no head nor eyes. The lophophore of Terebratulina septentrionalis (and 

 T. caput serpentis ?) is at first orbicular. The former has no provisional setae, 

 but has an apical tuft of cilia. 



The Testicardines differ from the Ecardines in becoming fixed before the 

 formation of the shell and in the relatively late appearance of the lophophore. 

 The last fact, coupled with the early atrophy of the head, may perhaps explain the 

 share taken by the dorsal mantle-fold in the formation of the lophophore. In the 

 larvae of Ecardines, supposing F. Miiller's larva to be rightly allocated to that sub- 

 order, the lophophore is a disc with the mouth in its centre, free from the dorsal 

 valves, and in Miiller's larva protrusible. It may be noted (i) that the lophophoral 

 circle of Brachiopoda always passes ventrally to the mouth ; it is therefore post- 

 oral ; (2) that the segmentation of the body is not comparable to that, e. g. of 

 Chaetopoda, and does not affect the mesoderm. 



The Brachiopoda are divisible into two orders. 



I. Ecardines (= Pleuropygia, Tretenteratd] : shell not composed of oblique 

 calcareous prisms ; no hinge ; no calcareous support for the lophophore ; an anus 

 which is either lateral or, as in Crania, posterior. 



The existing families are the Lingulidae with the two genera Lingula and 

 Glottidia ; Discinidae with Discina ; and Craniadae with Crania ; the extinct 

 families are two, the Obolidae and Trimerellidae, almost exclusively Silurian. 



II. Testicardines {=-Apygia, C Us tenter ata) : shell composed of oblique cal- 

 careous prisms ; a hinge nearly always well developed ; a cardinal process to the 

 dorsal valve. The living genera have no anus. 



(1) Eleutherobranchia (Neumayr) : no (free) brachial support. Orthidae s. 

 Strophonemidae, and Productidae, both extinct families, nearly confined to post- 

 Cambrian Palaeozoic strata. 



(2) Pegmatobranchia (Neumayr), with a (free) brachial support. The two 

 living existing families are the Rhynchonellidae, with one living genus Rhynchonella, 

 and many extinct, which are- principally Palaeozoic ; and the Terebratulidae with 

 living genera Argiope, Thecidium, Terebratulina, Terebratula, Waldheimia, Tere- 

 bratella, Megerlea, and a few others ; together with extinct genera, partly Palaeozoic, 

 partly Mesozoic. Wholly extinct families are the Koninckinidae, partly Palaeozoic, 

 partly Mesozoic ; the Spiriferidae, for the most part Palaeozoic, and the Atrypidae 

 and Stringocephalidae wholly so. 



Recent Brachiopoda, Davidson, Tr. L. S. (2), iv. pt. i, 1886. Lingula (Glot- 

 tidia] pyramidata, Beyer, Studies Biol. Laboratory, John's Hopkins University, iii. 

 (5), 1886. Crania with notes on Discina, Joubin, 'Recherches sur 1'Anat. des 

 Brachiopodes Inarticule's,' A. Z. Expt. (2), iv. (2), 1886. Argiope, Schulgin, Z. W. Z. 

 xli. 1854; Shipley, Mitth. Zool. Stat. Naples, iv. 1883. Brachiopoda Testicardinia, 

 van Bemmelen, J. Z. xvi. 1883. Cf. Hancock, 'Organisation of Brachiopoda,' Ph. 

 Tr. 148, 1858, and Bronn, Klass. und Ordn. der Thierreichs, iii. (i), 1862. 



Classification, &c., Neumayr, ' Ueber Branchialleisten der Productiden,' Neues 

 Jahrb. fur Min. Geol., &c. ii. 1883. 



1 De Lacaze Duthiers assigns to the larva of this Brachiopod four segments. His first, how- 

 ever, is evidently the disc bearing the eyes, which is not reckoned by Kowalewsky as a segment. 



