Miss Agnes Crane — Evolution of the Brachiopoda. 109 



its culmination, or period of maximum development, in a faunal 

 epoch antecedent to the appearance of the true Lingida, which is 

 therefore not the most ancient form of all the Brachiopoda (38). 



Prof. W. K. Brooks had long since noted the Obolelloid shape of 

 the shell in the larval phases of recent Lingulce {Glottidia) (12), just 

 as a Linguloid phase of shell growth had been previously recognized 

 by Morse as characterizing an early stage of Terebratnlina septen- 

 trionnlis still living on the east coast of Maine (PL V. Figs. 8a, 8&, 

 and Fig. 9) (56, 57). 



When we consider the tendency to abbreviation, which is a 

 general feature of later embryological stages, it is astonishing that 

 palseontologists should have been able to trace so many satisfactory 

 genealogies. 



The Lower Silurian true Lingulce gave rise to many generic rami- 

 fications, some of which were short-lived. Two genera — Lingula 

 and the divergent Glottidia — survive in existing oceans, the first on 

 the eastern, the second on western shores, both in shallow waters. 



Some of the early Lingulelloids, such as Lingulella (PI. V. Fig. 4) 

 and Lingulepis, fore-runners of Lingula, were of a very mixed type, 

 having the outward form of Lingula combined with the narrow 

 pedicle slit and simple muscular arrangements of the antecedent 

 Obolelloids (38). While Trematobolus from the St. John group 

 has been described by Mr. G. F. Mathew as an " articulated 

 Brachiopod of the Inarticulate order," it combines the features 

 of Siphonotreta, Schizambon (Fig. 13), and Obolus in the ventral valve 

 and those of Ortliis in its dorsal valve (52, 53). 



Hall's new genus Barroisella, a lineal descendant of Silurian 

 Lingulce, is an illustration which survived in Devonian seas of one 

 way in which the hingeless loose valves approach the articulated 

 or attached valves. It presents so marked a specialization of the 

 deltidial callosities as to indicate their approximation for articulatino- 

 and interlocking purposes. This genus left no descendants. 



In Lingulops (PL V. Fig. 6) and Lingulasma, now raised into family 

 rank by Winchell and Schuchert (64), we get proofs of the influence 

 of physiological causes on the origin of genera. They are said to be 

 "platform bearing" Lingulce, outwardly resembling Lingula, while 

 their internal structure yields evidence of their actual relationship 

 with the Silurian Trimerelloids. It took a Canadian (Dr. Billings), 

 several Americans (Hall, Meek, Whitfield), a Swede (Dr. Lindstrom), 

 the canny Scot (Davidson), and that far-seeing Professor of Queen's 

 College, Galway, William King, a slayer of Eozoon organism, and 

 one of the most philosophical of British writers on Brachiopoda, to 

 decipher the enigma of these strange fossils. I was present at their 

 introduction to the scientific world. The structure and affinities 

 of the group were first made known in detail at the Brighton 

 Meeting of the British Association in 1872, when Davidson read 

 a joint paper by himself (32) and William King (49), and James 

 Hall led the discussion. 



These thick-shelled Trimerelloids may, perhaps, be regarded as 

 the " dyspeptics " of the Brachiopod race, inasmuch as the large size 



