402 The American Geologist. june, isos 
before the publication of Huxley's "Introduction to the Classification of 
Animals." In England it is generally conceded that the priority and 
scope of Owen's orders were clearly established by the American syste- 
matist, Dr. Theodore Gill, The matter, however, is of less moment 
now that a general tendency to admit greater ordinal subdivision has 
arisen. Waagen has proposed six orders, Neumayr eight, and Beecher 
four, based on the peduncular opening and associated characters. 
The names Inarticulata and Articulata express certain general dis- 
tinctions. Nevertheless, it is a matter of fact that forms have often 
appeared which cannot be separated thus, for tendencies to transgress 
these artificial limits become apparent in various directions. For in- 
stance, the species of the Silurian genus Trime?'elta was shown by David- 
son and King to be but feebly articulated, and now Neoholns, Spon- 
dylobolus, and Hall's new linguloid genus BaiToisella, are shown to 
exhibit the same propensity. We are glad to note that,although fifteen 
years have elapsed since the publication of the Memoir on the Trimerel- 
lidce,hy Thomas Davidson and William King,* it is frankly admitted 
that later observations have hitherto added comparatively little to the 
results achieved by those eminent investigators and have taken away 
nothing from their value. 
In the present publication the semi-artificial, but convenient, family 
designations are not adopted, but the genera discussed fall into groups 
of associated genera, often exhibiting intermediate characters, which 
link one genus naturally with another. More has been accomplished 
in this direction than could possibly have been anticipated, and the 
eighth volume of the Geological Survey of the State of New York 
(Paleontology) would have made glad the heart of Darwin, for its dom- 
inent note is the evolution of genera. 
Hitherto Lingida has always been regarded as taxonomically at the 
base of the Brachiopoda, in spite of the acknowledged complexity of its 
muscular system and the date of its appearance in the geological series. 
It is now shown conclusively to be developed from an obolelloid type 
which culminated in a faunal epoch anterior to the appearance of Lin- 
gula, and Brooks' history of the development of the living species is 
cited as confirmatory proof of the direct obolelloid derivation of the 
paleozoic Lingulw from Obolella. Lingulella and Li?if/HZcpis,forerunners 
of Lingula, may be found to be important connecting links, having the 
outward form of linguloids with the muscular arrangements and narrow 
pedicle slit of the obolelloids. "The development on the linguloid line 
has continued, as we believe, from early Silurian to the present time 
with frequent modifications. From Lingula we may depart in many 
directions. In Lingulopf^ and Lmgnhtsma we get indications of physio- 
logical influences on the origin of genera." 
It appears that "augmented muscular energy and concomitant in- 
creased secretion of muscular fulcra," with the large size and consequent 
displacement of the liver, induced the thickening of ihe entire area of 
*Quarterly Journal of the Geological Society of London, vol. xxx, p. 
124, 1874. 
